absolute timing of sulfide and gold mineralization a comparison of re os molybdenite and ar ar mica methods from the tintina gold belt alaska new re os molybdenite dates from two lode gold deposits of the tintina gold belt alaska provide direct timing constraints for sulfide and gold mineralization at fort knox the re os molybdenite date is identical to the u pb zircon age for the host intrusion supporting an intrusive related origin for the deposit however 40ar 39ar dates from hydrothermal and igneous mica are considerably younger at the pogo deposit re os molybdenite dates are also much older than 40ar 39ar dates from hydrothermal mica but dissimilar to the age of local granites these age relationships indicate that the re os molybdenite method records the timing of sulfide and gold mineralization whereas much younger 40ar 39ar dates are affected by post ore thermal events slow cooling and or systemic analytical effects the results of this study complement a growing body of evidence to indicate that the re os chronometer in molybdenite can be an accurate and robust tool for establishing timing relations in ore systems

formation and palaeozoic evolution of the gorny altai altai mongolia suture zone south siberia zircon u pb constraints on the igneous record abstract the altai sayan fold belt epitomises how phanerozoic island arc continental crust contributed to the growth of the palaeo eurasian continent its formation is dominated by the closure of the palaeo asian ocean pao when island arc systems and gondwana derived terranes accreted to the siberian margin relics of the pao related tectonic units and associated granitoids occur along the ophiolitic charysh terekta ulagan sayan suture ctuss between gorny altai and altai mongolia zircon la icp ms u pb dating of this igneous record constrains the multi stage geodynamic pao evolution primitive kuznetsk altai island arc crust formed at the siberian margin during the ediacaran early cambrian 525 555 ma this island arc matured during the middle late cambrian 510 ma and was consumed by pao subduction in the late cambrian early ordovician 480 490 ma forming the siberian early caledonian accretion collision belt south of the ctuss granitic magmatism occurred within gondwana derived altai mongolia during the middle late ordovician 450 470 ma palaeo kazakhstan assembly and during a silurian early devonian 400 425 ma andean type collision middle late devonian 360 395 ma granitoids were emplaced as a result of the collision of altai mongolia with siberia during final pangaea amalgamation the suture was strike slip reactivated associated magmatism 295 ma the youngest 220 255 ma sampled granitoids originated in an intra plate setting

a tale of amalgamation of three permo triassic collage systems in central asia oroclines sutures and terminal accretion the central asian orogenic belt records the accretion and convergence of three collage systems that were finally rotated into two major oroclines the mongolia collage system was a long n s oriented composite ribbon that was rotated to its current orientation when the mongol okhotsk orocline was formed the components of the kazakhstan collage system were welded together into a long single composite arc that was bent to form the kazakhstan orocline the cratons of tarim and north china were united and sutured by the beishan orogen which terminated with formation of the solonker suture in northern china all components of the three collage systems were generated by the neoproterozoic and were amalgamated in the permo triassic the central asian orogenic belt evolved by multiple convergence and accretion of many orogenic components during multiple phases of amalgamation followed by two phases of orocline rotation

zircon u pb and hf isotopic study of gneissic rocks from the chinese altai progressive accretionary history in the early to middle palaeozoic abstract gneissic rocks in the chinese altai mountains have been interpreted as either paleozoic metasedimentary rocks or precambrian basement this study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a ne sw traverse in the northwestern chinese altai petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from i type granites formed in a subduction environment three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 ma some give neoproterozoic ages and a few yield discordant paleoproterozoic to archean ages zircon hf isotopic compositions indicate that both juvenile mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived in contrast zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids and define single populations for each sample with mean ages between 380 and 453 ma the general absence of precambrian inheritance and positive zircon hf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas our data can be interpreted in terms of a progressive accretionary history in early to middle palaeozoic times and the chinese altai may possibly represent a magmatic arc built on a continental margin dominated by neoproterozoic rocks

the tectonic evolution of the irtysh tectonic belt new zircon u pb ages of arc related and collisional granitoids in the kalaxiangar tectonic belt nw china abstract precise geochronological constraints of the irtysh tectonic belt situated between the saur island arc and the altay terrane are crucial to a better understanding of the tectonic evolution of the central asian orogenic belt caob recently we discovered repeatedly deformed arc related and collisional granitoids in the kalaxiangar tectonic belt ktb which is located in the eastern part of the irtysh tectonic belt in this study we report new whole rock geochemical zircon u pb and hf isotopic data of the arc related and collisional granitoids our data reveal that 1 arc related granodioritic porphyries formed at ca 382 374 ma recrystallized zircon grains from a ultra mylonitic granodiorite of the laoshankou zone in the southern ktb display a u pb age of ca 360 ma 2 syn collisional granodioritic porphyries which distribute along faults and parallel to the cleavage were emplaced at ca 367 356 ma with e hf t values varying from 7 8 to 14 2 and hf model ages from 873 to 459 ma 3 a post collisional a type granodioritic porphyry which crosscuts the nw nnw trending schistosity of the metasedimentary country rocks at a low angle has an age of ca 324 320 ma while the e hf t values range from 7 6 to 14 4 with hf model ages from 850 to 416 ma 4 post collisional strike slip a type granite dykes exposed along strike slip faults gave ages between 287 and 279 ma whereas the e hf t values range from 4 9 to 12 7 and the hf model ages from 995 to 500 ma and 5 a type biotite granite dykes which intruded along conjugate tension joints have ages of 274 271 ma and e hf t values from 1 5 to 13 2 with hf model ages from 1196 to 454 ma consequently we propose that the collision between the saur island arc and the altay terrane occurred in the early carboniferous ca 367 356 ma and the subsequent post collisional tectonic process continued to the late carboniferous ca 324 320 ma it is further suggested that the irtysh tectonic belt underwent large scale strike slip deformation during the mid permian between 287 and 279 ma the termination of the irtysh tectonic belt orogeny is thought to have also occurred during the mid permian between 274 and 271 ma

a synthesis of zircon u pb ages and hf isotopic compositions of granitoids from southwest mongolia implications for crustal nature and tectonic evolution of the altai superterrane abstract granitoid magmatism is extensively developed in the altai superterrane but the timing of magmatic events is not so well determined in this study twelve granitoid intrusions from southwest mongolia were dated by the zircon u pb method and analyzed for zircon hf isotopic compositions the new age data indicated three phases of magmatic emplacement middle paleozoic 398 350 ma late paleozoic 317 289 ma and triassic ca 244 211 ma the first phase magmatism is mainly composed of hornblende bearing i type granitoids formed during a long lasting subduction process in the early to middle paleozoic the second phase magmatism was manifested by a few small intrusions primarily distributed along the erqis fault zone and probably formed in a transitional tectonic regime from subduction to post tectonic setting in the late paleozoic the third phase magmatism was represented by post tectonic granitoids emplaced in an intraplate extensional setting model ages that were calculated using the composition of new continental crust are predominantly neoproterozoic to early paleozoic indicating that the protoliths of granitoids were likely dominated by paleozoic juvenile crust with minor neoproterozoic materials the altai superterrane was a huge paleozoic tectonic collage produced by amalgamation of subduction accretion complexes in the margin of the siberian continent and the tuva mongol microcontinent

tornado days in the united states by phase of the madden julian oscillation and global wind oscillation tornado activity in the united states varies over multiple time scales the madden julian oscillation mjo and global wind oscillation gwo are sources of climate variability at the seasonal and subseasonal scales the univariate distributions of tornado days across the phases of these oscillations have been documented but the bivariate distribution of tornado days across both oscillations has not been here the bivariate distribution of tornado days across the phases of the mjo and gwo is documented and analyzed results herein refine the previously reported univariate distributions and highlight variability across the phases of one of the oscillations while holding the phase of the other constant e g tornado days are more likely during phase 2 of the gwo but the likelihood varies across the phase of mjo

acoustic emission uncovers thermal damage evolution of rock abstract the thermal damage evolution of rock closely relates to many important scientific and engineering problems such as the mechanisms of earthquake and the effective extraction of deep geothermal energy however there is lack of rational thermal damage evolution model and the mechanisms of thermal damage are still unclear especially during cooling by use of a specially designed acoustic emission ae test system we explored the thermal damage evaluation in a rock and established a thermal damage evolution model which takes into account both heating and cooling processes the mechanisms of rock damage caused by heating and cooling were analyzed by using a lattice spring model and two different microstructural explanations were found i e heterogeneous microstructure and microdefect structure the damage evolution model can be used for more accurate modeling of these problems which involve rock thermal damage such as induced seismic activity during deep geothermal exploration

fragments of oceanic islands in accretion collision areas of gorny altai and salair southern siberia russia early stages of continental crustal growth of the siberian continent in vendian early cambrian time abstract the altai salair area in southern siberia is a caledonian folded area containing fragments of vendian early cambrian island arcs in the vendian early cambrian an extended system of island arcs existed near the paleo asian ocean siberian continent boundary and was located in an open ocean realm in the present day structural pattern of southern siberia the fragments of vendian early cambrian ophiolites island arcs and paleo oceanic islands occur in the accretion collision zones we recognized that the accretion collision zones were mainly composed of the rock units which were formed within an island arc system or were incorporated in it during the subduction of the paleo asian ocean under the island arc or the siberian continent this system consists of accretionary wedge fore arc basin primitive island arc and normal island arc the accretionary wedges contain the oceanic island fragments which consist of oib basalts and siliceous carbonate cover including top and slope facies sediments oceanic islands submerged into the subduction zone and later were incorporated into an accretionary wedge collision of oceanic islands and island arcs in subduction zones resulted in reverse currents in the accretionary wedge and exhumation of high pressure rocks our studies of the gorny altai and salair accretionary wedges showed that the remnants of oceanic crust are mainly oceanic islands and ophiolites therefore it is important to recognize paleo islands in folded areas the study of paleo islands is important for understanding the evolution of accretionary wedges and exhumation of subducted high pressure rocks

the atmospheric angular momentum cycle during the tropical madden julian oscillation abstract global scale wind and outgoing longwave radiation anomalies are documented during the atmospheric angular momentum aam cycle associated with the madden julian oscillation cross spectral and compositing techniques are applied to 150 and 850 mb national meteorological center wind data and outgoing longwave radiation olr data during ten northern winter and summer seasons coherent wind and olr signals are found in the tropics and in the winter hemisphere and are dominated by zonal wavenumbers 0 2 at the time of zero aam anomaly anomalous zonal winds are found over the western hemisphere tropics during northern winter while convection anomalies tend to be collocated with the seasonal mean australasian convection zonal mean olr anomalies are small as the aam anomaly increases the anomalous zonal winds move eastward and poleward while dipole convection anomalies become established over the oceanic warm pool and result in an east west shift of the australasian monsoon zonal mean olr ano

the thermo tectonic history of the song kul plateau kyrgyz tien shan constraints by apatite and titanite thermochronometry and zircon u pb dating abstract the song kul basin sits on a plateau at the northern and middle kyrgyz tien shan junction it is a lacustrine basin occupied by lake song kul and predominantly developed on igneous basement this basement was targeted for a multi method chronological study to identify the different magmatic episodes responsible for basement formation and to constrain the timing of the development of its present day morphology zircon u pb dating by la icp ms revealed four different magmatic episodes a late cambrian 500 ma island arc system a late ordovician 450 ma subduction related intrusion an early permian 290 ma collisional stage and a middle to late permian 260 ma post collisional magmatic pulse middle to late triassic 200 230 ma titanite fission track ages and late triassic early jurassic 180 210 ma apatite fission track ages and thermal history modeling indicate the song kul basement was already emplaced in the shallow crust at that time an exhumed fossil apatite fission track partial annealing zone is recognized in the bordering song kul mountain ranges the area experienced only minor post early mesozoic denudation the igneous basement was slowly brought to apatite u th he retention temperatures in the late cretaceous palaeogene miocene to present reactivation of the tien shan does not manifestly affect this part of the orogen

the influence of co2 on the solubility of quartz in single phase hydrothermal fluids implications for the formation of stockwork veins in porphyry copper deposits

paragenesis and re os molybdenite age of the cambrian ak sug porphyry cu au mo deposit tyva republic russian federation the ak sug porphyry cu au mo deposit is situated within the altai sayan region that forms part of the tuva mongol arc of the central asian orogenic belt the ak sug intrusive complex is made up of a series of nested intrusions including diorite feldspar porphyry quartz feldspar porphyry tonalite i and tonalite ii cu au mo mineralization occurs mainly within quartz carbonate k feldspar sulfide veins and later sericite sulfide veins and alteration in the northern zone sulfide zoning consists of a central bornite core flanked by chalcopyrite and pyrite chalcopyrite zones with a pyrite zone on the hanging wall side re os molybdenite dating of an early stage quartz carbonate k feldspar sulfide vein and a late stage molybdenite only vein gives ages of 517 3 3 and 517 4 3 ma respectively this indicates an early cambrian age for mineralization at ak sug making it one of the oldest porphyry copper deposits in the central asian orogenic belt published whole rock geochemical data indicate that intrusive rocks at ak sug and other cambrian to early ordovician intrusive complexes in the tuva mongol arc evolved by hornblende titanite fractionation due to high magmatic water contents leading to adakite like compositions with high sr y and flat to listric shaped rare earth element patterns that characterize many fertile arc magmas

isotope provinces mechanisms of generation and sources of the continental crust in the central asian mobile belt geological and isotopic evidence abstract the available geological geochronological and isotopic data on the felsic magmatic and related rocks from south siberia transbaikalia and mongolia are summarized to improve our understanding of the mechanisms and processes of the phanerozoic crustal growth in the central asian mobile belt camb the following isotope provinces have been recognised precambrian t dm 3 3 2 9 and 2 5 0 9 ga at the microcontinental blocks caledonian t dm 1 1 0 55 ga hercynian t dm 0 8 0 5 ma and indosinian t dm 0 3 ga that coincide with coeval tectonic zones and formed at 570 475 420 320 and 310 220 ma continental crust of the microcontinents is underlain by or intermixed with juvenile crust as evidenced by its isotopic heterogeneity the continental crust of the caledonian hercynian and indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments the crustal growth in the camb had episodic character and important crust forming events took place in the phanerozoic formation of the camb was connected with break up of the rodinia supercontinent in consequence of creation of the south pacific hot superplume intraplate magmatism preceding and accompanying permanently other magmatic activity in the camb was caused by influence of the long term south pacific plume or the asian plume damping since the devonian

cu and mo re enrichment during ductile deformation a case study of the yuleken porphyry cu deposit eastern junggar nw china abstract porphyry cu deposits can be strongly deformed during subsequent tectonic evolution to date research pertaining to the deformation and the enrichment of mineralization in porphyry deposits has suffered from a paucity of proof here we describe the diagnostic petrologic and geochemical signatures of the yuleken porphyry cu deposit from stages of metallogenic overprinting the rocks studied in this work are from deformation metallogenic structures that have 1 a distinguished metallogenic and tectonic evolution 2 a three layer spatial deformation metallogenic structure 3 distinguishably different fluid components within protomylonite mylonite and ultramylonite zones and 4 variational geochemical characteristics of coexisting chalcopyrite and magnetite integrated sulfide and oxide mineral investigations pertaining to the mineral deformation and the trace element variation of the minerals chalcopyrite and magnetite in the yuleken porphyry cu deposit indicated that cu and mo can be enriched during ductile deformation through physical analogous geochemical characteristics of chalcopyrite from different stages and chemical migrations the elemental variation of magnetite magnetites from deformed stages have higher contents of ti v co mn and ga than those from other stages and the variation of the fluid components within the protomylonite mylonite and ultramylonite zones reveal that the migration and precipitation of cu mo and fe were influenced by oxygen fugacity fluid components and temperature variation in conclusion the arc related porphyry deposits were able to become involved in the ductile deformation zone inducing areas of cu and mo enrichment in theory units subjected to ductile deformation may have great potential for porphyry cu mo deposit formation under the influence of magmatism

zircon u pb geochronology and hf isotopic composition of granitiods in russian altai mountain central asian orogenic belt the central asian orogenic belt caob consists of many tectonic terranes with distinct origin and complicated evolutionary history understanding of individual block is crucial for the reconstruction of the geodynamic history of the gigantic accetionary collage this study presents zircon u pb ages and hf isotopes for the granitoid rocks in the russian altai mountain range including gorny altai altai mongolian terrane and ctus suture zone between them in order to clarify the timing of granitic magmatism source nature continental crustal growth and tectonic evolution our dating results suggest that granitic magmatism of the russian altai mountain range occurred in three major episodes including 445 429 ma 410 360 ma and 241 ma zircons from these granitoids yield comparable positive ehf t values and neoproterozoic crustal model ages which favor the interpretation that the juvenile crustal materials produced in the early stage of the caob were probably dominant sources for the paleozoic magmatism in the region the inference is also supported by widespread occurrence of short lived juvenile materials including ophiolites seamount relics and arc assemblages in the northern caob consequently the paleozoic massive granitic rocks maybe do not represent continental crustal growth at the time when they were emplaced but rather record reworking of relatively juvenile proterozoic crustal rocks although mantle derived mafic magma was possibly involved to serve as heat engine during granitic magma generation the early triassic granitic intrusion may be a product in an intra plate environment as the case of same type rocks in the adjacent areas the positive ehf t values 1 81 7 47 and corresponding hf model ages 0 80 1 16 ga together with evidence of petrology are consistent with the interpretation that the magma source of the triassic granitic intrusion was derived from enriched mantle and melted under an usually high temperature condition likely due to basaltic magma that underplated the lower crust our data combined with evidence of the regional geology enable us to conclude that the gorny altai and altai mongolian terranes possibly have similar tectonic natures but represent two separate accretionary systems before devonian collision the accretion and amalgamation processes resulted in the paleozoic granitoid magmatism and caused the two terranes to merge as a composite tectonic domain at the siberian continental margin

madden julian oscillation induced suppression of northeast pacific convection increases u s tornadogenesis abstractthis study investigates the impact of the madden julian oscillation mjo on u s tornadogenesis using atmospheric reanalysis and model experiments our analysis shows that the impact of mj

the ca 350 ma beja igneous complex a record of transcurrent slab break off in the southern iberia variscan belt abstract we report the results of an isotopic study of the large gabbro dioritic beja igneous complex bic in the boundary between the highly contrasting ossa morena om and south portuguese sp zones of the southern iberian variscan orogen this boundary is interpreted as a major suture zone materialized by discontinuous scattered strips of mafic ultramafic rocks the so called beja acebuches ophiolite complex baoc and by melange deposits of middle to late devonian age in the pulo do lobo accretionary prism plap the beja gabbro was interpreted either as part of the ophiolite like units or as a broadly arc related massif reflecting the northward subduction of oceanic lithosphere u pb zircon id tims dating of two diorites and a granodiorite points to igneous emplacement ages of 350 2 ma serpa 352 2 ma torrao and 353 4 ma sao pedro respectively whereas a felsic dyke yields a slightly younger age of 345 2 ma these results show that published ar ar dates do not represent igneous crystallization ages but merely reflect regional cooling below ca 500 c at least 10 ma after the major intrusive event probably as a result of uplift of the omz side of the suture zone relative to the subsiding spz 87sr 86sr350 and end350 display a large range of values from 0 7041 to 0 7093 and from 4 0 to 6 1 respectively which documents a rather complex petrogenetic history with an important role played by crustal contamination processes the more primitive sr and nd isotope signatures are measured in the mafic cumulates while radiogenic sr and unradiogenic nd isotope compositions occur in the more evolved rock types the broad trend of decreasing end350 with decreasing sm nd and increasing sio2 concentration is reminiscent of crustal assimilation combined with fractional assimilation afc end values of flasergabbros and associated cumulates ascribed to the ophiolite like unit in the guadiana valley are close to zero or even slightly negative irrespective of the age chosen for the correction for in situ radioactive decay of 147sm in the range 350 500 ma assumed to encompass the true geological age this observation conflicts with a truly oceanic derivation of these rocks which could rather represent early stage deformed and metamorphosed equivalents of the beja gabbro most metabasalts of the same area have positive albeit variable end consistent with mildly depleted mantle sources and or significant crustal assimilation only a few samples reach highly positive values end350 500 ca 8 similar to those typical for n morbs as do the acebuches amphibolites near aracena end350 500 ca 9 these data suggest that the baoc is not only disrupted but also composite since the gabbroic rocks are not cogenetic with the basalts based on the late devonian age of the collision between the omz and spz the emplacement of the beja gabbro cannot be related to an active subduction of oceanic lithosphere instead the generation in the mantle and emplacement in the overlying continental crust of copious volumes of mafic magmas with concomitant lp ht metamorphism is tentatively ascribed to a process of transcurrent slab break off that followed oblique subduction and collision

paleoproterozoic accretionary orogenesis in the north china craton a shrimp zircon study abstract the inner mongolia suture zone imsz and the trans north china orogen tnco incorporate the major paleoproterozoic accretionary orogens in the north china craton ncc with the jiao liao ji belt jljb representing the third one here we investigate the paleoproterozoic tectonics of the imsz and tnco through zircon shrimp geochronology on a representative suite of rocks comprising metasediments and arc magmatic rocks shrimp analysis of zircons with textures indicating extreme recrystallization under ultrahigh temperature uht conditions from the metapelites at heling er in the southern domain of the imsz reveals a single population with a weighted mean 207 pb 206 pb age of 1913 17 ma the zircons in another uht granulite from this locality yield a weighted mean 207 pb 206 pb age of 1910 18 ma these data correlate with the ca 1 92 ga age reported from zircons in sapphirine bearing uht granulites further north and confirm the regional extent of the paleoproterozoic uht metamorphism within the imsz zircons in a charnockite from the southern margin of the khondalite belt fringing the uht granulites in the imsz show two distinct age groups an older population with a magmatic paragenesis and a weighted mean 207 pb 206 pb age of 1932 24 ma and a younger group of metamorphic zircons with an age of 1858 26 ma we also report zircon ages from charnockites in two localities around xing he in the huangtuyao belt belonging to the huai an complex within the westernmost domain of the tnco at the junction with the imsz the charnockite from first locality carries two distinct zircon populations with the older group yielding a weighted mean 207 pb 206 pb age of 2477 2 ma and the younger population showing an age of 1807 38 ma the internal structure as revealed from cl images and the overall high th u values up to 2 42 of the older zircons suggest their magmatic affinity whereas the younger group with extremely low th u 0 02 0 09 is of metamorphic origin zircons from the charnockite in the second locality also define two distinct age clusters with a dominant older magmatic group having a weighted mean 207 pb 206 pb age of 2147 11 ma and a minor younger group with an age of 1958 25 ma the range of ages from 2477 to 2147 ma from magmatic zircons in the charnockites from the eastern periphery of the imsz within the western margin of the tnco in combination with similar ages reported in recent studies from zircons in magmatic complexes within the imsz suggest a prolonged history of subduction related arc magmatism and accretionary tectonics analogous to those in some of the phanerozoic belts such as the central asian orogenic belt and the western pacific subsequent progressive collision and suturing of the continental blocks were accompanied by the exhumation of high pressure hp and uht metamorphic rocks the available data from the imsz and tnco suggest long lived convergent margins associated with the southward subduction of the yinshan block and westward subduction of the eastern block in a double sided subduction realm prior to the final amalgamation of the ncc and its incorporation within the columbia supercontinent in the late paleoproterozoic

palaeozoic accretionary and convergent tectonics of the southern altaids implications for the growth of central asia the southern altaids present a unidirectional section from mongolia to china through an accretionary orogen that youngs progressively from neoproterozoic in the north to permian in the south the orogen formed by forearc accretion of island arcs accretionary wedges ophiolites and precambrian microcontinents this regularity was upset by early growth within the ocean of arcs that later collided at the accreting continental margin by imbrication of old ophiolites with young arcs and by himalayan style thrust nappe tectonics when an arc collided into a microcontinent lateral growth of the southern altaids represents a massive addition of juvenile material to the palaeozoic crust

neoproterozoic to paleozoic geology of the altai orogen nw china new zircon age data and tectonic evolution abstract we present a synthesis and a new account of the geological and tectonic history of the terranes of the chinese paleozoic altai orogen together with new single zircon ages for granitic and rhyodacitic rocks a central terrane consists of neoproterozoic to silurian amphibolite facies metasedimentary rocks and abundant devonian carboniferous granites the presence of precambrian basement is indicated by sinian fossils our xenocryst ages and published nd mean crustal residence ages of granites felsic arc type lavas on the southern margin of the terrane have a mean 207pb 206pb zircon age of 505 ma reflecting the time of arc volcanism and the presence of xenocysts with ages between 614 and 921 ma suggests derivation by intracrustal melting accordingly we suggest that a cambro ordovician continental magmatic arc was built on the southern margin of the central terrane by northward subduction a low grade ordovician andean type arc with a continental basement is situated above a normal fault on

revisiting the irtish tectonic belt implications for the paleozoic tectonic evolution of the altai orogen abstract the irtish tectonic belt is one of the most important suture zones in the central asian orogenic belt caob the various models invoked to explain the tectonic evolution of this belt in relation to paleozoic continental growth include 1 syn subduction strike slip duplication of a single long lived arc and 2 collision of many arcs and micro continents here we report new results from detailed field studies geochemistry and zircon u pb geochronology on the major rock units along the irtish belt both in kazakhstan and in the chinese altay our new results together with information from published data suggest that the altai mongolia terrain witnessed several episodes of subduction the junggar terrain which formed by multiple collisions of intra oceanic arcs seamounts and ophiolite suites prior to 330 ma subsequently amalgamated with the altai mongolia terrain at around 320 ma along the irtish suture zone following the clockwise rotation of the siberian craton and the n directed movement of the junggar terrain the sinistral strike slip motion along the irtish suture zone resulted in ductile shearing partial melting of the crustal material and the formation of mylonites syn tectonic migmatite and gneissic granites the sinistral strike slip deformation of the irtish suture zone culminated at ca 275 ma the diverse 275 250 ma magmatism mafic ultramafic complexes bimodal intrusives mafic and silicic dykes a type and i a type granites is related to magma pulses generated by the permian tarim mantle plume our model of multiple episodes of subduction below the altai arc is different from previous models and proposes that the subduction continued until triassic with the permian subduction under the altai arc and a late permian large scale south directed thrusting

replication of internal defects and investigation of mechanical and fracture behaviour of rock using 3d printing and 3d numerical methods in combination with x ray computerized tomography abstract it is difficult to accurately visualize internal structure and characterize progressive fracture process during rock failure due to the heterogeneous and opaque features of rock this paper focuses on providing two methods i e 3d printing 3dp and 3d numerical modelling to replicate internal defects and study the mechanical and fracture behaviours of rock in combination with x ray computerized tomography micro ct on one hand stereolithography 3dp combined with the x ray micro ct and 3d reconstruction techniques were applied to replicate natural volcanic rocks using 3dp resin uniaxial compression and brazilian disc tests were subsequently performed to characterize and visualize the mechanical and fracture properties of the 3dp rock on the other hand the digital image processing technique was adopted to integrate the microstructures of the natural volcanic rock into the rock failure process analysis code rfpa3d digital for characterizing the failure behaviour of rock under uniaxial compression and tension the results showed that both the 3dp samples and the 3d numerical models can successfully replicate the internal defects and micro structures identical to those of the natural prototype volcanic rock the mechanical properties of the 3dp samples and the 3d numerical models including compressive and tensile strength and the poisson s ratio and fracture properties are testified to be similar to those of the prototype rocks visualization analysis of the progressive fracture process demonstrated that the initial internal voids and cracks dominate the spatial fracture evolution and failure patterns within the rock the proposed methods provide a promising means to quantify replicate and visualize the pre existing defects and mirco structures and to understand their influences on the mechanical and fracture behaviour of rock under different loading conditions facilitating better understanding of failure mechanism of rocks

the crustal assembly of southern mongolia new structural lithological and geochronological data from the nemegt and altan ranges abstract the gobi altai region is an ideal setting for studying processes of continental growth and subsequent intracontinental and intraplate deformation including terrane accretion and dispersal ophiolite obduction crustal reactivation and intraplate mountain building to assess the diverse tectonic evolutionary models of the gobi altai and the wider region more field data and geochronological data are required to constrain the tectonic evolution of individual terranes and the relationship of adjacent crustal domains to each other throughout time in this paper we present new lithological structural and 40ar 39ar age data which constrain the crustal evolution across a previously unreported late paleozoic terrane boundary in the gobi altai nemegt and altan nuruu are topographically linked mountain ranges that were formed by miocene recent uplift at a right stepping restraining bend along the left lateral gobi tien shan fault system in southern mongolia ordovician carboniferous arc rocks and an ophiolite are exposed in the mountain ranges and form a small part of the east west arcuate trans altai zone field observations of rock types and structures combined with petrographic data are used to distinguish metamorphosed volcano sedimentary arc rocks in altan nuruu and western nemegt nuruu from arc rocks in central and eastern nemegt nuruu these distinct sequences are correlated with the dzolen and edrengin terranes in the trans altai zone along strike to the west integration of field data 40ar 39ar age data and published studies are used to describe a polyphase deformation history that includes late carboniferous ophiolite obduction mid permian to late triassic shortening and lateral terrane redistribution cretaceous rifting and late cenozoic intraplate mountain building

crustal melting and magma mixing in a continental arc setting evidence from the yaloman intrusive complex in the gorny altai terrane central asian orogenic belt abstract granitoids and their hosted mafic enclaves may retain important information on crust mantle interaction and thus are significant for study of crustal growth and differentiation an integrated petrological geochronological and geochemical study on the granitoid plutons of the yaloman intrusive complex from the gorny altai terrane northwestern central asian orogenic belt was conducted to determine their source nature petrogenesis and geodynamics mafic enclaves are common in the plutons and a zircon u pb age 389 ma 4 ma indicates that they are coeval with their granitoid hosts ca 393 387 ma petrographic observations reveal that these mafic enclaves probably represent magmatic globules commingled with their host magmas the relatively low sio2 contents 46 0 60 7 wt and high mg 38 9 56 5 further suggest that mantle derived mafic melts served as a crucial component in the formation of these mafic enclaves the granitoid hosts including quartz diorites and granodiorites are i type in origin possessing higher sio2 contents 60 2 69 9 wt and lower mg 32 0 44 2 their zircon hf and whole rock nd isotopic compositions indicate that the magmas were dominated by remelting of neoproterozoic 0 79 1 07 ga crustal materials meanwhile the geochemical modeling together with the common occurrence of igneous mafic enclaves and the observation of reversely zoned plagioclases suggests that magma mixing possibly contributed significantly to the geochemical variation of the granitoid hosts our results imply that mafic magmas from the mantle not only provided substantial heat to melt the lower crust but also mixed with the crust derived melts to form the diverse granitoids the oxidizing and water enriched properties inferred from the mineral assemblages and compositions imply that the granitoid plutons of the yaloman intrusive complex were possibly formed in a continental arc related setting which is also supported by their geochemistry the devonian granitoids from the gorny altai terrane show remarkable temporal spatial petrogenetic affinities to the counterparts from the altai mongolian terrane indicating that these two terranes were possibly under subduction of the same oceanic plate i e the ob zaisan ocean the voluminous granitoids signify significant crustal recycling and growth as a response to the underplating of extensive mantle derived basaltic melts

occurrence of phosphatic microfossils in an ediacaran cambrian mid oceanic paleo atoll limestone of southern siberia abstract new phosphatic microfossils were recently discovered in an ediacaran cambrian mid oceanic paleo atoll limestone in the southern gorny altai mountains in southern siberia microfossils with calcium phosphate shells are abundant in the limestone that occurs as an exotic block within a cambrian accretionary complex in the kurai area sem observations confirm that the calcium phosphatic shells are ellipsoidal and equal sized about 200 300 m in diameter shell walls are about 1 m thick as the absence of external and internal structures hinders a detailed comparison identification these microfossils are tentatively treated here as paleontological problematica epma analysis confirmed the concentration of elements p and ca in microfossil shells and the absence in the matrix suggesting the primary phosphatic composition of the shells because phosphatic microfossils are generally scarce in the ediacaran but abundant from the lower cambrian in particular within pre trilobitic ssf assemblages the phosphatic fossil bearing limestone in the kurai area possibly belongs to the lower cambrian the present find proves that mid oceanic paleo seamounts as well as continental shelf domains had already been inhabited by diverse metazoans in the ediacaran cambrian transitional interval

tectonic evolution in the archaean and proterozoic kre high heat flow probably favoured global hotspot activity with crustal growth of iceland type through vertical magmatic accretion the tectonic environment for the generation of about 3 9 2 5 ga granite gneiss greenstone terrains with volurnlnous production of tonalite trondhjemite granodlorite magmas is still uncertain and both piate ma and intrapiate scenarios arc possible deformanon atylea in greenstones and adjacent high grade orthognersses with intercalated shallow water supracrustal assemblages suggest extensive horizontal shortening and crustal interstacking this probably resulted from collisional and or rotational motion and produced significant intracrustal melting as early as 3 9 ga by the end of the archaean and locally much earlier crustal thicknesses reached 35 50 km or more and the cxtl aordinary hhlding to erogenic deformation may have been due to delamination and crustal subduction towards the end of the proterozoic evidence for modern style plate tectonics becomes abundant through the recognition of laland a16 accretion ophiolite obducdon foreland thrust and fold belts and exotic terranes one of the best documented example for this tectonic environment is the arabian nubian shield 4lthough it is doubtful whether modern plate tectonic settings can serve as analogues for all precambrian tectonic styles it i clear that global crustal evolution since the early archaean was governed by the motion of plates which repeatedly came togethel tv fotm supercontinents and then dlspersetl again we shall not understand the detailed mechanism of precambrian crustal itlton cs before we learn horn lo irltejpret recent large scale crustal deformation and its causes

architecture and mineral deposit settings of the altaid orogenic collage a revised model abstract the altaids are an orogenic collage of neoproterozoic paleozoic rocks located in the center of eurasia this collage consists of only three oroclinally bent neoproterozoic early paleozoic magmatic arcs kipchak tuva mongol and mugodzhar rudny altai separated by sutures of their former backarc basins which were stitched by new generations of overlapping magmatic arcs in addition the altaids host accreted fragments of the neoproterozoic to early paleozoic oceanic island chains and neoproterozoic to cenozoic plume related magmatic rocks superimposed on the accreted fragments all these assemblages host important many world class late proterozoic to early mesozoic gold copper molybdenum lead zinc nickel and other deposits of various types in the late proterozoic during breakup of the supercontinent rodinia the kipchak and tuva mongol magmatic arcs were rifted off eastern europe siberia and laurentia to produce oceanic backarc basins in the late ordovician the siberian craton began its clockwise rotation with respect to eastern europe and this coincides with the beginning of formation of the mugodzhar rudny altai arc behind the kipchak arc these earlier arcs produced mostly cu pb zn vms deposits although some important intrusion related orogenic au deposits formed during arc arc collision events in the middle cambrian and late ordovician the clockwise rotation of siberia continued through the paleozoic until the early permian producing several episodes of oroclinal bending strike slip duplication and reorganization of the magmatic arcs to produce the overlapping kazakh mongol and zharma saur valerianov beltau kurama arcs that welded the extinct kipchak and tuva mongol arcs this resulted in amalgamation of the western portion of the altaid orogenic collage in the late paleozoic its eastern portion amalgamated only in the early mesozoic and was overlapped by the transbaikal magmatic arc which developed in response to subduction of the oceanic crust of the paleo pacific ocean several world class cu mo porphyry cu pb zn vms and intrusion related au mineral camps which formed in the altaids at this stage coincided with the episodes of plate reorganization and oroclinal bending of magmatic arcs major pb zn and cu sedimentary rock hosted deposits of kazakhstan and central asia formed in backarc rifts which developed on the earlier amalgamated fragments major orogenic gold deposits are intrusion related deposits often occurring within black shale bearing sutured backarc basins with oceanic crust after amalgamation of the western altaids this part of the collage and adjacent cratons were affected by the siberian superplume which ascended at the permian triassic transition this plume related magmatism produced various deposits such as famous ni cu pge deposits of norilsk in the northwest of the siberian craton in the early mesozoic the eastern altaids were oroclinally bent together with the overlapping transbaikal magmatic arc in response to the northward migration and anti clockwise rotation of the north china craton the following collision of the eastern portion of the altaid collage with the siberian craton formed the mongol okhotsk suture zone which still links the accretionary wedges of central mongolia and circum pacific belts in the late mesozoic a system of continent scale conjugate northwest trending and northeast trending strike slip faults developed in response to the southward propagation of the siberian craton with subsequent post mineral offset of some metallogenic belts for as much as 70 400 km possibly in response to spreading in the canadian basin india asia collision rejuvenated some of these faults and generated a system of impact rifts

accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield kroner a windley b f badarch g tomurtogoo o hegner e jahn b m gruschka s khain e v demoux a and wingate m t d 2007 accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield in hatcher r d jr carlson m p mcbride j h and martinez catalan j r eds 4 d framework of continental crust geological society of america memoir 200 p 181 209 doi 10 1130 2007 1200 11 for permission to copy contact editing geosociety org 2007 the geological society of america all rights reserved kroner kroener mail uni mainz de windley brian windley btinternet com tomurtogoo igmr magicnet mn hegner hegner lmu de jahn jahn earth sinica edu tw khain khain ginras ru demoux demoux uni mainz de wingate mwingate tsrc uwa edu au

multi method chronometry of the teletskoye graben and its basement siberian altai mountains new insights on its thermo tectonic evolution

post late glacial calcareous tufas from the kurai fault zone southeastern gorny altai russia abstract calcareous tufa deposits have been discovered in the chibitka river valley near lake cheybek kohl at the junction of the kurai and teletsk kurai large active faults in the southeastern gorny altai russia at an altitude of 1800 2000 m fossil tufa is composed of calcite and cements holocene grey colluvium and glacial till deposited by the late glacial chibitka glacier current tufa precipitation has been observed from a low flow spring with cold 10 c hco 3 so 4 ca mg water 6 86 the stable isotope composition of spring water is 5 8 vpdb 13 c of dissolved inorganic carbon and 14 5 vsmow 18 o modern tufa consists of thin laminated mg calcite and sr aragonite crusts with abundant algae and biofilms on their surfaces both modern and fossil tufas are depleted in ree a total of 0 40 16 4 ppm and 0 40 3 80 ppm respectively and share similar paas normalised ree y spectra with hree enrichment and slight progressive lree depletion the modern tufas show positive 13 c values of 0 1 to 0 9 vpdb while the fossil ones have an isotopically lighter composition of 13 c 4 1 to 1 9 vpdb the 18 o range is very narrow 13 0 to 13 8 vpdb both stable isotope and trace element signatures including ree patterns of the tufas indicate precipitation from cold groundwaters subjected to prolonged interaction with a carbonate aquifer the baratal group of limestone and dolostone in a cold continental climate similar to the present conditions tufa deposition in the lake cheybek kohl area began with the onset of post late glacial global warming and permafrost degradation unlike the fossil tufa formation current precipitation of freshwater carbonates has been microbially mediated the discovered tufa deposits provide new palaeoclimatic and active tectonic proxies in the southeastern gorny altai

new insight into a subduction related orogen a reappraisal of the geotectonic framework and evolution of the japanese islands abstract the geotectonic framework and the evolutionary history of the japanese islands need revision in accordance with the various geophysical geological evidence gathered by new methodologies in the recent years including seismic tomography vibroseis ground breaking seismic experiments and detrital zircon chronology these investigations have addressed various themes such as 1 seismic profile of the crust and mantle beneath the japanese islands 2 high precision ages of the protoliths of high p t metamorphic rocks and 3 provenance of terrigenous clastics the results have led to a number of important findings including 1 detection of a large mass of slab around the mantle boundary layer suggesting the long term oceanic subduction beneath japan 2 confirmation of the subhorizontal piled nappe structure for the entire crust of japan 3 finding a new high p t metamorphosed accretionary complex unit that represents the youngest blueschist in japan 4 finding of the oldest early cambrian arc batholith and cover sediments and 5 the identification of plural arc batholiths which have already been erased from the surface based on a synthesis of these new data this article presents a re evaluation of the conventional geotectonic subdivision of the subduction related orogen in japan re definition of the elements and their mutual boundaries and re consideration of the geotectonic evolution of the japanese islands in particular the historical change in provenance suggests that proto japan has experienced large scale tectonic erosion in multiple stages and the corresponding large amounts of continental crust materials were subducted for understanding the orogenic growth of japan during the last ca 500 million years the significance of tectonic erosion coupled with continental contraction as well as the oceanward accretionary growth requires further attention

differences in the acoustic emission characteristics of rock salt compared with granite and marble during the damage evolution process rock salt cavities for energy storage are important elements of energy supply management and sustainability the mechanical properties of other common rocks have already been adequately investigated but a systematic characterization of the differences in acoustic emission ae characteristics among rock salt and other common rocks is needed in this study the ae characteristics of the full regime uniaxial compression of rock salt and common rocks such as granite and marble were determined a damage variable based on ae parameters and a methodology for its determination were established including an analysis of the characteristics of the ae time space evolution the ae amplitude distribution and the damage evolution based on ae parameters clear differences were observed in the ae characteristics of rock salt compared with granite and marble during the damage evolution process the ae activity and energy release of rock salt with coarse grains and nonuniform structures decreased gradually with increasing stress level the ae activity of rock salt appeared in a continuous group occurring form the ae spatial distribution of rock salt was relatively uniform without a definite rupture surface the ae amplitude distribution varied slowly and the proportion of ae events with small amplitudes increased gradually during compression in rock salt moreover the damage in rock salt predominantly occured during the pre peak period resulting in a large damage variable of 0 9 at peak stress by contrast the damage variables of granite and marble are only 0 5 and 0 1 respectively at peak stress rock salt exhibited less damage when approaching failure resulting in a gentler and steadier process and the plastic characteristics of rock salt are relatively obvious these properties to some extent ensure the safety of underground storage engineering when rock salt is chosen as the medium

geochemistry and geochronology of carboniferous volcanic rocks in the eastern junggar terrane nw china implication for a tectonic transition the carboniferous tectonic setting of the junggar terrane northern xinjiang nw china has long been a matter of debate voluminous carboniferous volcanic rocks are widely distributed in the karamaili area the southern part of the eastern junggar terrane early carboniferous rocks comprise basalts and basaltic andesites with enrichment of lree and lile and depletion of hfse and uniformly high end t 3 7 to 4 0 late carboniferous rocks consist of basalts basaltic andesites rhyolites and minor dacites and can be subdivided into basic and felsic groups the basic rocks are depleted in hfse and show variable high end t 4 8 to 6 9 they have higher cr and ni and lower na2o u and th contents than early carboniferous basic rocks the felsic rocks show a type affinity with typical enrichment of alkalis lree and hfse and strong depletion in ba sr eu and ti they have high values of end t and zircon ehf t 11 6 to 17 9 new la icpms zircon u pb analyses constrain their emplacement to late carboniferous time 306 5 314 3 ma the carboniferous basic rocks show negative zr hf anomalies and low th ce 0 07 and th la 0 06 0 16 excluding significant crustal contamination during magma evolution they have low la ba 0 03 0 12 ce y 3 and tb yb n 2 and variable ba th 28 318 and ba la 3 1 34 suggesting that they were derived from a main spinel with minor garnet lherzolite mantle source metasomatized by slab derived fluids the late carboniferous felsic rocks were produced when upwelling asthenosphere triggered partial melting of juvenile lower crust the early carboniferous volcanism occurred in an island arc setting related to the southward subduction of the paleo junggar ocean plate whereas the late carboniferous rocks erupted in a post collisional extensional setting thus a rapid tectonic transition from arc to post collisional extension may have occurred between early and late carboniferous and probably resulted from slab break off or lithospheric delamination

generalized crack initiation and crack damage stress thresholds of brittle rock masses near underground excavations abstract the rock mass failure process is characterized by several distinct deformation stages which include crack initiation crack propagation and coalescence it is important to know the stress levels associated with these deformation stages for engineering design and practice extensive theoretical experimental and numerical studies on the failure process of intact rocks exist it is generally understood that crack initiation starts at 0 3 to 0 5 times the peak uniaxial compressive stress in confined conditions the constant deviatoric stress criterion was found to describe the crack initiation stress level here generalized crack initiation and crack damage thresholds of rock masses are proposed the crack initiation threshold is defined by 1 3 a cm and the crack damage threshold is defined by 1 3 b cm for jointed rock masses where a and b are material constants and cm is the uniaxial compressive strength of the rock masses for a massive rock mass without joints cm is equal to cd the long term uniaxial strength of intact rock after examining data from intact rocks and jointed rock masses it was found that for massive to moderately jointed rock masses the material constants a and b are in the range of 0 4 to 0 5 0 8 to 0 9 respectively and for moderately to highly jointed rock masses a and b are in the range of 0 5 to 0 6 0 9 to 1 0 respectively the generalized crack initiation and crack damage thresholds when combined with simple linear elastic stress analysis assist in assessing the rock mass integrity in low confinement conditions greatly reducing the effort needed to obtain the required material constants for engineering design of underground excavations

some key issues in reconstructions of proterozoic supercontinents abstract supercontinents containing most of the earth s continental crust are considered to have existed at least twice in proterozoic time the younger one rodinia formed at 1 0 ga by accretion and collision of fragments produced by breakup of the older supercontinent columbia which was assembled by global scale 2 0 1 8 ga collisional events little consensus has been reached regarding configurations of these supercontinents because of some unresolved issues concerning continental fits one of these issues concerns how siberia was related to laurentia previous reconstructions that consider the aldan shield of siberia as a continuation of the wyoming province of laurentia have been largely abandoned in favor of models connecting siberia to northern laurentia but it remains controversial which part of siberia is contiguous with northern laurentia also at issue is the western laurentia australia east antarctica connection most rodinia reconstructions place australia together with east antarctica adjacent to either western canada the sweat hypothesis or the western united states the auswus hypothesis however recent studies combining paleomagnetic and isotopic age data have called into question the validity of sweat auswus and other variants another issue is the position of north china in rodinia columbia limited paleomagnetic data seem to be consistent with the paleo mesoproterozoic north china siberia baltica connection whereas geological data support the recently proposed archean to mesoproterozoic north china india connection controversial issues have also been raised about the timing and history of the amalgamation and fragmentation of south america and west africa both geological and paleomagnetic data suggest that south america sao francisco and amazonia cratons and west africa congo and west african cratons coalesced into a single landmass along the 2 1 2 0 ga transamazonian eburnean orogens however whether they were divorced and then re married to form part of gondwana or remained largely coherent from their amalgamation at 2 1 2 0 ga until their incorporation into gondwana is unclear also little known is the position of amazonia west africa in the proposed supercontinents with some workers believing that they existed as a separate landmass whereas others place amazonia west africa adjacent to baltica in summary although geological and paleomagnetic data are supportive of the existence of proterozoic supercontinents rodinia and columbia they are insufficient to determine their exact geometries

plate impact experiments to investigate shock induced inelasticity in westerly granite abstract in the present study plate impact experiments are employed to better understand the stress threshold for inelasticity in westerly granite the experiments are designed to obtain the hugoniot elastic limit hel as well as spall strength following shock induced compression in the westerly granite samples the hel for westerly granite is estimated to be in the range 3 2 to 3 5 gpa while the spall strength is 50 mpa for a pulse duration of 3 s and is nearly independent of the compression stress level in the stress range employed in the experiments i e 0 7 5 0 gpa in addition soft recovery plate impact experiments are employed to better understand the threshold for initiation of micro cracking in the granite samples these recovery experiments are conducted at the same stress levels as the normal plate impact experiments 0 7 gpa and the duration of the tensile pulse is varied from 20 to 500 ns by varying the pre set gap between the specimen and the momentum trap the results indicate that the stress pulse duration threshold for initiation of spall is about 120 ns at an applied tensile stress level of 0 7 gpa in addition tensile fracture in westerly granite is observed to be time dependent with the spall strength dependent on the duration of the tensile pulse for the soft recovery experiments that do not show a clear spall signal the recovered granite specimens show relatively large micro cracks 30 40 m in width near the plane where the unloading waves from the flyer and target free surfaces intersect the spall plane reveals a relatively rough and a tortuous fracture surface at higher magnifications several cracks and pits holes are detected on the spall plane the fracture damage mode is seen to be predominantly brittle with damage initiating at the weak grain boundaries

robustness of relations between the mjo and u s tornado occurrence abstractthe madden julian oscillation mjo is the leading mode of tropical variability on subseasonal time scales and has predictable impacts in the extratropics whether or not the mjo has a disc

dynamic model validation using blast vibration monitoring in mine backfill abstract sublevel stoping mining methods with delayed backfill are employed for mining steeply dipping ore deposits at deeper horizons cemented rockfill crf is used as a backfilling material for open stopes formed during mining in primary secondary mining sequence blast vibrations are induced in crf during the extraction of adjacent stopes higher magnitude of blast vibrations may destabilize crf causing failure and dilution of precious ore this paper presents a methodology for calibrating a flac3d numerical model encompassing mine backfill with blast induced vibration data recorded from field instrumentation two flac3d models are prepared one for simulating the blasting process and the other is prepared for backfill stability analysis the first model resulted in load vectors to be applied to backfill and rock interface the second model showed that the backfill fails under the blast vibrations induced by the adjacent production stope the results of the back analysis of fill failure are presented and discussed the methodology may serve as numerical model calibration procedure for mine backfill

further evaluation of the re os geochronometer in organic rich sedimentary rocks a test of hydrocarbon maturation effects in the exshaw formation western canada sedimentary basin abstract re os isotopic analyses of a single organic rich sedimentary rock unit ors of known depositional age and at three levels of regional hydrocarbon maturity show that hydrocarbon maturation does not affect the ability the 187re 187os chronometer to yield a depositional age for such rocks we present re os isotope analyses from the late devonian exshaw formation in the subsurface of the western canada sedimentary basin alberta and obtain a re os isochron age of 358 10 ma 2 model 3 1 666 10 11 a 1 for samples ranging from hydrocarbon immature to overmature this age is within uncertainty of the established absolute age for the exshaw formation hydrocarbon immature and mature plus overmature samples show no significant age differences if regressed individually indicating that hydrocarbon maturation did not greatly disturb the re os isotope system in the exshaw formation as such we propose that the re os geochronometer may be used as a reliable tool for measuring the depositional ages of ors regardless of their level of hydrocarbon maturity we find that minimizing natural variation in the initial 187os 188os ratio is more important than avoiding hydrocarbon maturation in obtaining precise re os ages in particular the exshaw formation appears to contain a nonhydrogenous component of unradiogenic os in addition to the hydrogenous os load a subset of exshaw formation samples with 5 total organic carbon toc which should best reflect the hydrogenous os load alone yields a very well fitted isochron having a depositional age of 358 9 ma 2 1 666 10 11 a 1 with an initial 187os 188os ratio of 0 59 0 05 model 3 mean square of weighted deviates mswd 1 8 the initial 187os 188os ratio of this regression may provide an estimate of the os isotopic composition of local seawater at the time of deposition

a reworked lake zone margin chronological and geochemical constraints from the ordovician arc related basement of the hovd zone western mongolia abstract the primary relationships and character of the boundaries between principal lithotectonic domains in the mongolian tract of the central asian orogenic belt caob are still poorly constrained this brings much uncertainty in understanding of the orogeny configuration and the complete accretionary history the plutonic khuurai tsenkher gol complex and the mainly metasedimentary bij group represent associated medium to high grade basement complexes exposed in the hovd zone close to its boundary with the lake zone in western mongolia the khuurai tsenkher gol complex is composed of variously deformed acid to basic magmatic rocks intimately associated with the metamorphosed sedimentary and volcanic rocks of the bij group results of our field work new u pb zircon ages and whole rock geochemical data suggest an existence of two separate magmatic events within the evolution of the khuurai tsenkher gol complex early to mid ordovician 476 5 ma and 467 4 ma protoliths normal to high k calc alkaline orthogneisses metadiorites and metagabbros predominate over mid silurian 430 3 ma tholeiitic mildly alkaline quartz monzodiorites whereas the geochemical signature of the former suite unequivocally demonstrates its magmatic arc origin that of the latter quartz monzodiorite suggests an intra plate setting as shown by sr nd isotopic data the older arc related magmas were derived from depleted mantle and or were generated by partial melting of juvenile metabasic crust detrital zircon age populations of the metasedimentary rocks together with geochemical signatures of the associated amphibolites imply that the bij group was a volcano sedimentary sequence formed probably in the associated fore arc wedge basin moreover our data argue for an identical provenance of the altai and hovd domains overall westward sediment transport during the early palaeozoic and the east dipping subduction polarity the obvious similarities of the khuurai tsenkher gol complex hovd zone with the neighbouring togtokhinshil complex lake zone suggest that both magmatic complexes originally belonged to the same magmatic arc related to the palaeo asian subduction system the geodynamic cause of the later within plate magmatic pulse is unclear but was probably still related to the effects of retreating subduction slab window ocean ridge subduction or back arc lithosphere thinning the khuurai tsenkher gol complex was subsequently separated from the western margin of the lake zone and imbricated into the hovd zone melange it is proposed that the lake hovd zones boundary in the study area represents a younger deformation zone rather than a true terrane boundary suture this could be a general feature of the suture zones within this part of the caob

correlational fractal characterisation of stress and acoustic emission during coal and rock failure under multilevel dynamic loading abstract the fractal characterisation of stress and acoustic emission ae of coal and rock failure may provide quantitative guidance for analysing the stability of rock mass during excavation engineering the correlation between stress and ae data was calculated using fractal theory methods and grassberger procaccia g p algorithms to evaluate the damage and degree of flaw in coal and rock materials under multilevel dynamic loading mdl first the mechanical properties of the testing device were developed to obtain synchronous data regarding the stress and aes of coal and rock specimens under mdl second strength deterioration behaviour and the felicity effect during coal and rock failure are compared under different levels of dynamic loading the results show that cumulative dynamic loading are less than the uniaxial compression strength of coal and rock the felicity effect is notable and felicity ratios decrease to 1 with increased loading velocity finally stresses and ae signals are considered as the data mining specimens of correlation dimensions based on the g p algorithm fractal characteristics on stress and ae coupling properties become more notable as the correlated dimensions become larger however the felicity effect is less prominent reflecting a lesser degree of damage and flaws in coal and rock materials therefore this study suggests a data mining method for the correlation dimension to be applied in an in situ monitoring system for rock mass excavation engineering

nd sr isotopic mapping of the chinese altai and implications for continental growth in the central asian orogenic belt article i nfo the chinese altai orogen is a typical domain of the central asian orogenic belt and in previous syntheses was divided into six tectonic units or terranes in this paper 41 new and 36 published whole rock nd and sr isotopic data for granitoid intrusions and mafic dykes within units 2 and 3 of the central altai and units 4 to 6 of the southern altai were used for isotopic mapping the age of the samples used is known from u pb zircon dating end t values range from 4 to 2 in the central altai units 2 and 3 and from 1 4 to 6 in the southern altai units 4 and 5 and up to 8 4 in unit 6 correspondingly nd model ages tdm decrease from 1 6 1 1 ga in the central altai to 1 0 0 5 ga in the southern altai except for a continental fragment in unit 4 isr is elevated in the central units decreasing to b0 705 in the southern units 5 and 6 these results demonstrate that the central altai contains widespread old crustal components in its basement whereas the southern altai comprises a higher proportion of juvenile crust when integrated with published u pb zircon ages our data show that new crust grew southwards in the chinese altai in addition our data suggest that units 2 and 3 are a single tectonic unit whereas the southern altai unit 4 which previously was regarded as a single young accretionary terrane should be subdivided into two units a younger arc and an older continental fragment the granitoids in the chinese altai can be divided into syn and post non orogenic groups the syn orogenic granitoids have ca 50 80 mantle derived component whereas the post non orogenic granitoids contain ca 70 90 the generation of syn and post non orogenic granitoids represents horizontal lateral and vertical crustal growth which contributed ca 18 28 and 7 8 respectively to the area of the chinese altai this work shows that isotopic mapping is an effective approach to elucidate terrane composition in the central asian orogenic belt and thereby better constrain palaeozoic crustal growth

progressive accretionary tectonics of the beishan orogenic collage southern altaids insights from zircon u pb and hf isotopic data of high grade complexes abstract high grade gneissic rocks of the southern altaids in central asia bear one of the key elements needed to solve a basic architectural controversy in accretionary orogenesis high grade gneissic rocks widely crop out across the beishan orogenic collage southern altaids mapped as the beishan complex or dunhuang group which was previously regarded as neoarchean to paleoproterozoic crystalline basement but without systematic field geochronological and geochemical data this study provides field geochemical and zircon u pb and hf isotopic data for gneissic rocks from the beishan complex geochemical data show that the gneissic rocks were probably formed in a subduction environment most zircons from the beishan complex are magmatic origins because their th u ratios are mostly in the range of 1 0 0 1 they show age peaks at 494 ma 464 ma and 375 ma with a few precambrian ages zircon hf isotopic compositions indicate that both old and juvenile materials were involved in the formation of the beishan complex which is different from the basement rocks of the tarim craton both in radiometric age and hf isotopic composition all these data thus do not support a uniform precambrian basement in the beishan area as previously proposed but instead the beishan complex probably formed in a subduction accretion environment combined with regional geology and geochemical data we conclude that the beishan orogenic collage was characterized by progressive long lived accretionary tectonics during late precambrian to paleozoic time therefore shedding light on the controversy regarding the architecture of accretionary orogens

late paleozoic faults of the altai region central asia tectonic pattern and model of formation abstract the present kinematic and dynamic analysis of large scale strike slip faults which enabled the formation of a collage of altai terranes as a result of two collisional events the late devonian early carboniferous collision of the gondwana derived altai mongolian terrane and the siberian continent resulted in the formation of the charysh terekta system of dextral strike slip faults and later the kurai and kuznetsk teletsk bashkauss sinistral strike slip faults the late carboniferous permian collision of the siberian and kazakhstan continents resulted in the formation of the chara irtysh and north east sinistral strike slip zones the age of deformation of both collisional events becomes younger toward the inner areas of the siberian continent in the same direction the amount of displacement of strike slip faulting decreases from several thousand to several hundred kilometers the width of the late paleozoic zone of deformation reaches 1500 km these events deformed the accretion collision continental margins and their primary paleogeographic pattern

use of correlation fractal dimension signatures for understanding the overlying strata dynamics in longwall coal mines abstract the longwall mining is considered to be the best coal mining practices due to vast recovery of coal over other forms of underground as well as opencast mining methods but the actual scenario is quite opposite in india where productivity form of the longwall mines lags far behind than the desired level irregular caving and sudden rock bursts which are very hazardous for mine workers and equipment usually these are major problem faced by bulk of indian longwall faces and which are due to the presence of thick sandstone beds as overlying strata thus to keep an eye on the rock bursts it is very necessary to monitor the stressed zones in the hanging overlying strata above and behind the panel earlier correlation integral c and correlation fractal dimension dc has been very helpful in monitoring the stressed zones for several great earthquakes in past following the same way in the present study we have used the mine induced microseismic data obtained from the retreating longwall panel using various monitoring instruments to calculate the correlation fractal dimension dc for monitoring the stress levels and fractures in the overlying strata and also for spatio temporal forecasting of roof falls the variation of blast charge size with fractal dimension is also studied the use of fractal dimension has been very effective in obtaining the precursory signatures for roof fall thus ensuring safety in the mines

variability of central united states april may tornado day likelihood by phase of the madden julian oscillation 1 april may tornado day likelihood from 1990 to 2011 was calculated for the central united states for phases of the madden julian oscillation mjo an april tornado day was found more likely during mjo phases 6 and 8 and less likely during phases 3 4 and 7 a may tornado day was found more likely during phases 5 and 8 and less likely in phases 2 and 3 during phases with above normal tornado day likelihoods positive anomalies of convective available potential energy bulk vertical wind shear and storm relative helicity were found in the central united states negative anomalies were found during phases with below normal tornado day likelihoods anomalies of such environmental parameters were connected to the mjo via variability in tropospheric circulation these results provide an important starting point for extended range prediction of u s tornado activity

accretionary orogenesis of the chinese altai insights from paleozoic granitoids zircon u pb dating and whole rock major oxide trace element and nd sr isotope compositions have been determined for four representative granitic intrusions in the sw chinese altai in order to understand the orogenesis and history of crustal growth in the central asian orogenic belt caob the ashile and halatas bodiesare relatively small intrusions formed in the late carboniferous 318 6ma andpermian 267 4ma respectively thelargertarlang tb andkeketuohaibatholiths kb havemagmaticagesof 359 to 412 ma the granitoids consist chiefly of tonalite granodiorite and granite and are metaluminous to weakly peraluminous in composition asi 0 8 1 1 the ashile pluton is characterized by relatively high mgo 2 73 3 54 wt and sr 395 456 ppm contents with low k2o na2o ratios 0 31 0 42 and mantle like nd sr isotopic compositions endt 2 85 to 3 26 initial 87 sr 86 sr 0 7047 0 7051 it probably formed by fractional crystallization of a mantle derived magma with limited assimilation of oldcrustalmaterial theotherintrusionshavenear zeroornegative endtvalues 0 67to 4 41 andhighersrisotopiccompositions initial 87 sr 86 sr 0 7067 0 7092 indicating a mixture of juvenile and old components in their genesis these intrusions are characterized by relatively low k rb cs contents and low rb sr ratios mostly b0 6 and generally exhibit moderate to high heavy rare earth element hree concentrations ybn 8 26 and weak hree fractionation dy ybnb1 5 with or without negative europium anomalies eu eu 0 5 1 0 these characteristics are consistent with an origin by dehydration melting of a hornblendebearing mid crustal source above the garnet stability field dominated by mafic to intermediate rocks this suggests that the deep crust of the chinese altai may contain a considerable proportion of juvenile material mantle derived magmatism probably in an active extensional continental margin setting played an important role in the formation of the chinese altai acting not only as a heat sourceforcrustalmeltingbutasasourceofjuvenilecomponents therelativelysmallvolumesanddistinctgeochemicalcompositions of the ashile and halatas plutons may imply a substantial change in the geodynamic setting in the late paleozoic 2007 elsevier b v all rights reserved

fractal property of spatial distribution of acoustic emissions during the failure process of bedded rock salt abstract a rock mechanics test system and the acoustic emission ae test system were employed to perform experiments on bedded rock salt samples under uniaxial compression and indirect tension based on the basic theory of fractal geometry a column covering method is proposed to analyze the fractal property of the spatial distribution of acoustic emissions during the rock damage and failure process the experimental results indicate obvious differences in failure features for different parts of a sample due to the structural differences in bedded rock salt the consistency between the failure state and the ae spatial distribution is confirmed the relationships of the stress and energy release with the fractal dimension of the ae spatial distribution are established an increase in the fractal dimension corresponds to a decrease in the stress and an increase in the energy release which is consistent with the theoretical analysis when the fractal dimension obtained from uniaxial compression and indirect tensile tests is less than 2 20 and 2 57 respectively the stresses in the bedded rock salt sample are over 80 of the peak stress a great amount of accumulated damage occurs leading to the global failure of the bedded rock salt sample therefore it is possible to forecast the failure state of bedded rock salt by inspecting the variation between the stress or the energy release and the fractal dimension of the ae spatial distribution

formation of the kokchetav subduction collision zone northern kazakhstan insights from zircon u pb and lu hf isotope systematics abstract the kokchetav subduction collision zone is located in the western part of the ancestral central asian orogenic belt this zone is built up by the precambrian kokchetav microcontinent which includes a hp uhp metamorphic belt and the north kokchetav tectonic zone nktz which represents an accretionary complex between the kokchetav microcontinent and the adjacent stepnyak island arc the entire region is widely intruded by palaeozoic granitoids which were emplaced after the collision of the stepnyak island arc with the kokchetav microcontinent we present zircon u pb ages and lu hf systematics in zircon to better characterize the tectonic evolution of the kokchetav subduction collision zone the lu hf results indicate that the kokchetav basement rocks are derived from late neoarchaean early palaeoproterozoic 2 5 ga crust for the granite gneiss basement of the kokchetav microcontinent early mesoproterozoic grenville age 1 17 1 14 ga zircon u pb crystallization ages were obtained for the nktz two main age components were recognized 1 an oldest mesoproterozoic age component 1 20 1 05 ga similar as for the kokchetav microcontinental zircons and 2 a younger early cambrian 540 520 ma or late cambrian early ordovician 490 480 ma age component th u ratios 0 1 and are typical of a magmatic protolith the distinction between both zircon types is supported by characteristic cathodoluminescence images these results confirm previous observations indicating early palaeozoic high grade metamorphism 540 520 ma and collisional deformation 490 480 ma of the mesoproterozoic kokchetav zone as a result of subduction accretion and collision of the stepnyak island arc to the kokchetav microcontinent for two additional samples of the balkashin granitic complex early devonian 415 395 ma zircon crystallization ages magmatic th u ratios were obtained the occurrence of a mesozoic xenocryst within these leucogranites may indicate that they were emplaced in a continental arc setting

comparative position of bateny and biya katun terrains altai sayan folded area russia in cambrian based on combined paleomagnetic lithologic and paleontological data abstract cambrian events in the history of the different terranes comprising mosaic block geological structures of the altai sayan folded area is discussed on the basis of the complex analysis of the paleontological lithological and paleomagnetic data the probable territorial proximity of the biya katun gorny altai and bateny kuznetsky alatau blocks is proved

the neoproterozoic evolution of the western siberian craton margin u pb hf isotopic records of detrital zircons from the yenisey ridge and the prisayan uplift abstract we present new la icp ms u pb hf detrital zircon data from neoproterozoic sedimentary basins located along the south western margin of the siberian craton in the yenisey ridge the taseeva basin siliciclastic sedimentary units contain abundant 2 7 2 5 ga 2 0 1 75 ga and 0 95 0 57 ga detrital zircon populations whereas for the prisayan uplift slightly different detrital zircon ages of 3 0 2 5 ga 2 2 1 8 ga and 0 95 0 65 ma are common mid neoproterozoic sandstones were deposited in a rift setting or along a rifted cratonic margin facing a back arc basin whereas the immature to submature upper ediacaran to lower cambrian fluvial successions were probably deposited in the foredeep setting at the expense of proximal neoproterozoic igneous suites and the underlying metasedimentary basement a range of ehf values from 10 to 14 indicates intense mixing between juvenile and evolved magma components in a continental arc setting at ca 950 570 ma geological evidence persistent input of detrital zircon material derived from ancient crustal units of western siberian cratonic margin and evolution of hf isotopic compositions suggest that the neoproterozoic arc system of the yenisey ridge and partly sayan orogens developed along the active margin of siberia in the neoproterozoic the arc system probably extended along the periphery of rodinia into the taimyr orogen of northern siberia and valhalla orogen of north eastern laurentia

a vendian cambrian island arc system of the siberian continent in gorny altai russia central asia an extended vendian cambrian island arc system similar to the izu bonin mariana type is described in the gorny altai terrane at the margin of the siberian continent three different tectonic stages in the terrane are recognized 1 a set of ensimatic active margins including subducted oceanic crust of the paleo asian ocean the uimen lebed primitive island arc oceanic islands and seamounts the set of rocks is assumed to be formed in the vendian 2 a more evolved island arc comprising calc alkaline volcanics and granites a fore arc trough in middle late cambrian time was filled with disrupted products of pre middle cambrian accretionary wedges and island arcs 3 collision of the more evolved island arc with the siberian continent folding metamorphism and intrusion of granites occurred in late cambrian early ordovician time in the late paleozoic the above mentioned caledonian accretion collision structure of the siberian continent was broken by large scale strike slip faults into several segments this resulted in the formation of a typical mosaic block structure

structural overprints of early paleozoic arc related intrusive rocks in the chinese central tianshan implications for paleozoic accretionary tectonics in sw central asian orogenic belts abstract the chinese central tianshan constitutes the centric and vital component of the tianshan orogen it contains important information for understanding the accretionary orogeny of the central asian orogenic belt caob to better constrain the paleozoic evolution of the chinese central tianshan we present new field observations fabric analyses zircon u pb ages zircon lu hf isotopic and whole rock geochemical data of mafic intermediate and felsic intrusive rocks in the baluntai area chinese central tianshan field scale and microscopic structural patterns of the intrusive rocks reveal that the early paleozoic gabbro diorite intrusions underwent multistage structural reworking and generally exhibit gently south or north dipping foliations and microscopic kinematic fabrics indicating top to the north shearing these ductilely deformed intrusive rocks were intruded by granitic sills or dikes that are generally sub parallel or with low angle to the main foliations of the host rocks gentle foliations and top to the north kinematics can be rarely noticed within the granitic intrusions at the sites close to the baluntai fault locally intense mylonitization occurred in the felsic intrusions and deformed mafic intermediate ones where earlier shallow foliations were completely or partially transformed to steep ones bearing sub horizontal stretching lineations and asymmetric kinematic indicators suggest dextral shearing zircon la icp ms u pb datings constrain the emplacement ages of the gabbroic and dioritic intrusive rocks at 452 420 ma and the crystallization age of one mylonitic k granite at 417 ma two samples of granitic sill contain plenty of zircons inherited from the host gabbroic and dioritic rocks and a few such zircons have dark rims probably formed during granitic injection dating on these rims roughly constrains the crystallization ages of the felsic sills at ca 370 360 ma the ehf t values of a gabbro 420 ma two diorite samples 425 and 445 ma and a mylonitic granite 417 ma vary from 15 45 to 2 06 corresponding to two stage crustal model ages tdm c ranging from 2 4 ga to 1 5 ga suggesting variable degrees of involvement of the proterozoic crustal basement and the juvenile mantle components during the early paleozoic magmatic generation the geochemical data of the mafic intermediate plutons exhibit features of magmatic rocks formed in continental arcs the mylonitic granite and one undeformed granite resemble a type granite in terms of geochemical features suggesting that these granites were produced in a post collisional extensional environment considering the previously published data the early paleozoic arc type magmatic rocks within the chinese central tianshan likely resulted from the southward subduction of an oceanic basin located to the north and ceased progressively during 420 400 ma the amalgmation between chinese central tianshan and tarim most likely completed at ca 360 ma following the closure of the south tianshan back arc basin this event reworked the chinese central tianshan arc and formed the top to the north kinematics thereafter the chinese central tianshan was affected by the early permian dextral strike slip faulting due to the regional large scale transcurrent tectonics and overprinted by the permian mafic magmatism

configuration of the late paleoproterozoic supercontinent columbia insights from radiating mafic dyke swarms abstract remnants of 2 1 1 8 ga orogens can be recognized in nearly every craton assembled within reconstructions of the rodinia supercontinent although no particular pattern of laterally extensive orogenic belts emerges these cratons may be the fragments of an older supercontinent formed in response to the collision and accretion of even older cratons during the early earth history paleomagnetic constraints have played a limited role in many previous reconstructions of the early precambrian supercontinent mainly because of the poor age control and a large scatter of the paleomagnetic poles the geometry of giant radiating dyke swarms and orogenic belts provide important constraints for the reconstruction of the pre rodinian supercontinent some early unmetamorphosed and undeformed mafic dyke swarms in north china southern peninsular india and north america share coeval age of 1 85 ga if these continents are assembled the overall pattern exhibited by the mafic dyke swarms appears to constitute a giant radiating swarm with a piercing point between the cuddapah rift in south india and the xiong er aulacogen in north china this suggests that the north china craton indian craton and canadian shield may be fragmented from the same landmass the reconstruction of 1 85 ga giant radiating dyke swarm attempted in this paper suggests that the north china craton india craton and canadian shield were united together to form a landmass within the columbia supercontinent before its extension and break up the 1 90 1 85 ga andean style north orogenic belt suggests that a subduction zone existed on the northern margin of the north china craton wopmay orogenic belt developed in a 1 88 1 84 ga continental volcano plutonic arc which is interpreted as the product of eastward subduction of oceanic lithosphere the transantarctica orogenic belt in east antarctica may be another candidate to be linked with the subduction zone the north orogenic wopmay orogenic and transantarctica orogenic belts could be connected to form a continuous subduction zone the orogenic comparison strengthens the configuration of the columbia supercontinent proposed by the reconstruction of the giant radiating dyke swarm the laurentia west australia and east antarctica were relatively stable from 1 85 ga to 1 20 ga as inferred from the data on dyke swarms magmatism and the paleomagnetism these continents constituted the core of the columbia supercontinent in the late paleoproterozoic time the north china craton and indian craton were however separated from the columbia supercontinent during the mesoproterozoic time

a re os study of sulfide minerals from the bagdad porphyry cu mo deposit northern arizona usa rhenium and osmium isotopes in sulfide minerals from the bagdad porphyry cu mo deposit have been used to determine timing of mineralization and the source of osmium and by inference ore metals molybdenite chalcopyrite and pyrite were analyzed mainly from the quartz monzonite and porphyritic quartz monzonite units which are characterized by moderate to strong potassic alteration secondary biotite and k feldspar rhenium concentrations in molybdenite are between 330 and 642 ppm four re os analyses of two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite yield a weighted average age of 71 8 0 2 ma 2 analyses of a third sample from a molybdenite vein in precambrian rocks outside of the main ore zone yield a weighted average age of 75 9 0 2 ma 2 and provide evidence of two separate mineralization episodes chalcopyrite samples contain 6 to 12 ppt os and 1 7 to 4 1 ppb re 187os 188os initial ratios are between 0 1 and 0 8 pyrite samples have osmium and rhenium concentrations varying in the range 8 17 ppt and 3 9 6 8 ppb respectively analyses from these pyrite samples yield an eight point isochron with an age of 77 15 ma 2 and an initial 187os 188os ratio of 2 1 0 8 mswd 0 90 the results presented here add to the growing body of work indicating that porphyry type mineralization is produced by long term multiple episodes of magmatism and associated mineralization the data also support the hypothesis that a significant part of the metals and magmas may have a crustal source as has been suggested for other copper deposits and districts in arizona

late paleozoic post collisional magmatism in the eastern tianshan belt northwest china new insights from geochemistry geochronology and petrology of bimodal volcanic rocks abstract the late carboniferous to permian marks an important phase of terrane amalgamation through accretion collision in the central asian orogenic belt caob the tianshan belt forms part of this sequence where the post collisional event generated an e w trending bimodal volcanic zone that extends for ca 500 km from the southern bogda mt to the easternmost tianshan belt here we report the petrology geochemistry and geochronology of the bimodal volcanic rocks to characterize the post collisional tectonic evolution in late paleozoic the major element chemistry of the basalt and rhyolite samples indicates a bimodal high k calc alkaline affinity the basalts are characterized by high abundance in tio2 th u and pb and depletion in nb ta and p together with slight enrichment in lree contents and low hfse lree ratios the rhyolites show a close affinity to aluminous a type granites with enrichment in k na zr ce y and depletion in p nb ta and ti they also exhibit fractionated ree patterns with prominent negative eu anomalies the petrographic and geochemical data suggest that this bimodal rock series was generated in a post collisional setting the mafic rocks are likely derived from a metasomatized lithospheric mantle assimilation of different crustal components played a minor role in the genesis of these basaltic rocks the la icp ms analysis on zircons from four rhyolites and two basalts yielded similar ages ranging from 295 8 2 8 to 293 3 1 7 ma suggesting an early permian event zircons from the basalts show a wide ehf t range from 0 49 to 13 whereas those from the rhyolites show two groups of ehf t values from 5 to 3 and from 6 to 12 suggesting a mixing of crust mantle material the magmatic zircons from the bimodal volcanic rocks yielded two peaks of tdm2 between 600 820 ma and 1160 1360 ma probably representing two significant episodes of continental crust growth the bimodal volcanic rocks are correlated with the early stage of post collision our results suggest that vertical crustal growth through mantle derived magmas in post collisional setting also played a major role in the construction of the caob

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

neoproterozoic middle paleozoic tectono magmatic evolution of the gorny altai terrane northwest of the central asian orogenic belt constraints from detrital zircon u pb and hf isotope studies abstract the gorny altai terrane ga is a key area in understanding the crustal evolution of the central asian orogenic belt caob this paper reports u pb and hf isotope data for detrital zircons from cambrian to early devonian sedimentary sequences to constrain their provenance as well as the tectono magmatic events and crustal growth in this region nearly all the detrital zircons are characterized by euhedral to subhedral morphology high th u ratios ca 0 1 1 6 and typical oscillatory zoning indicating a magmatic origin the three samples from the gorny altai group middle cambrian to early ordovician yield detrital zircon populations that are composed predominantly of 530 464 ma grains followed by a subordinate group of 641 549 ma old the silurian and devonian samples exhibit similar major zircon populations 555 456 ma and 525 463 ma respectively but a significant amount of additional 2431 772 ma zircons occur in the early devonian sample our results suggest that detritus from the nearby kuznetsk altai intra oceanic island arc served as a unitary source for the cambrian silurian sedimentary sequences but older detritus from other sources added to the early devonian sequence the low abundance of ca 640 540 ma detrital zircons may testify that this island arc was under a primitive stage in this period when mafic volcanic rocks probably dominated in contrast the dominant population of ca 530 470 ma zircons may indicate an increased amount of granitic rocks in the source area suggesting that the kuznetsk altai island arc possibly evolved into a mature one in the cambrian to early ordovician the ca 530 470 ma detrital zircons are almost exclusively featured by positive e hf t values and have two stage hf model ages of ca 1 40 0 45 ga indicating that the precursor magmas were sourced predominantly from heterogeneous juvenile materials we conclude that the late neoproterozoic to early paleozoic magmatism in the kuznetsk altai arc made a significant contribution to the crustal growth in the caob the absence of middle ordovician to early devonian detrital zircons possibly implies that the area changed to a passive margin in the middle ordovician of special significance are the 2431 772 ma zircons in the early devonian sample which are quite comparable to the precambrian detrital zircons from the altai mongolian terrane am but distinct from those from the siberian continent this indicates that the am is a plausible source for the 2431 772 ma zircons our data therefore imply that the ga possibly amalgamated with the am before the early devonian rather than in the late devonian to early carboniferous as previously suggested

geodynamics and metallogeny of the central eurasian porphyry and related epithermal mineral systems a review abstract major porphyry cu au and cu mo deposits are distributed across almost 5000 km across central eurasia from the urals mountains in russia in the west to inner mongolia in north eastern china these deposits were formed during multiple magmatic episodes from the ordovician to the jurassic they are associated with magmatic arcs within the extensive subduction accretion complex of the altaid and transbaikal mongolian orogenic collages that developed from the late neoproterozoic through the palaeozoic to the jurassic intracratonic extension the arcs formed predominantly on the palaeo tethys ocean margin of the proto asian continent but also within two back arc basins the development of the collages commenced when slivers of an older proterozoic subduction complex were rifted from an existing cratonic mass and accreted to the palaeo tethys ocean margin of the combined eastern europe and siberian cratons subduction of the palaeo tethys ocean beneath the karakum and altai tarim microcontinents and the associated back arc basin produced the overlapping late neoproterozoic to early palaeozoic tuva mongol and kipchak magmatic arcs contemporaneous intra oceanic subduction within the back arc basin from the late ordovician produced the parallel urals zharma magmatic arc and separated the main khanty mansi back arc basin from the inboard sakmara marginal sea by the late devonian the tuva mongol and kipchak arcs had amalgamated to form the kazakh mongol arc by the mid palaeozoic the two principal cratonic elements the siberian and eastern european cratons had begun to rotate relative to each other drawing in the two sets of parallel arcs to form the kazakh orocline between the two cratons during the late devonian to early carboniferous the palaeo pacific ocean began subducting below the siberian craton to form the sayan transbaikal arc which expanded by the permian to become the selanga gobi khanka arc by the middle to late permian as the kazakh orocline continued to develop both the sakmara and khanty mansi back arc basins were closed and the collage of cratons and arcs were sutured by accretionary complexes during the permian and triassic the north china craton approached and docked with the continent closing the mongol okhotsk sea an embayment on the palaeo pacific margin to form the mongolian orocline subduction and arc building activity on the palaeo pacific ocean margin continued to the mid mesozoic as the indosinian and yanshanian orogens significant porphyry cu au mo and au cu deposits were formed during the ordovician in the kipchak arc e g bozshakol cu au in kazakhstan and taldy bulak porphyry cu au in kyrgyzstan silurian to devonian in the kazakh mongol arc e g nurkazgan cu au in kazakhstan and taldy bulak levoberezhny au in kyrgyzstan devonian in the urals zharma arc e g yubileinoe au cu in russia devonian in the kazakh mongol arc e g oyu tolgoi cu au and tsagaan suvarga cu au in mongolia carboniferous in the kazakh mongol arc e g kharmagtai au cu in mongolia tuwu yandong cu au in xinjiang china koksai cu au kounrad cu au and the aktogai group of cu au deposits in kazakhstan carboniferous in the valerianov beltau kurama arc e g kal makyr dalnee cu au in uzbekistan benqala cu au in kazakhstan late carboniferous to permian in the selanga gobi khanka arc e g duobaoshan cu au in inner mongolia china triassic in the selanga gobi khanka arc and jurassic in the selanga gobi khanka arc e g wunugetushan cu mo and jiguanshan mo in inner mongolia china in addition to the tectonic geologic and metallogenic setting and distribution of porphyry cu au mo mineralisation within central eurasia the setting geology alteration and mineralisation at each of the deposits listed above is described and summarised in table 1

precambrian crystalline basement in southern mongolia as revealed by shrimp zircon dating single zircon ages determined by ion microprobe shrimp ii for granitoid gneisses from the southern slope of the baga bogd massif gobi altai southern mongolia reveal several episodes of zircon growth ranging from late palaeoproterozoic to late cambrian the oldest events are documented by a zircon crystallization age for a gneiss protolith at 1519 11 ma and by a xenocrystic zircon from a dark grey augen gneiss yielding an age of c 1701 ma discrete igneous events are recorded in granite gneisses with protolith emplacement ages of 983 6 956 3 and 954 8 ma these ages provide the first record of early neoproterozoic magmatic activity in this region a much younger and discrete magmatic event is recorded by several dioritic to granitic orthogneisses which are tectonically interlayered with the older gneisses and have protolith emplacement ages between 502 and 498 ma these late cambrian granitoids of calc alkaline affinity are likely to have been emplaced along an active continental margin and suggest that the baga bogd precambrian crustal fragment was either docked against the southward present day coordinates growing margin of the caob or was a large enough crustal entity to develop an arc along its margin we speculate that the precambrian gneisses of this massif may be part of a crustal fragment rifted off the tarim craton

dynamic stress concentration and energy evolution of deep buried tunnels under blasting loads abstract a theoretical formulation was first established to evaluate the dynamic stress concentration factor dscf around a circular opening under conditions of blasting stress wave incidence a two dimensional numerical model was then constructed by the particle flow code pfc in order to simulate the dynamic responses around an underground tunnel subjected to blasting load in the simulation a series of horizontal blasting stress waves were applied to an underground tunnel under various in situ stress states and then the dynamic responses around the tunnel were analyzed from the viewpoint of the dynamic stress concentration and energy evolution the results of theoretical analysis indicated that obvious dynamic effects occur at tunnel boundary during blasting stress wave incidence and the dscf at the roof and floor of the tunnel is much larger than that at two sidewalls when blasting stress wave was applied to left model boundary the numerical results showed that high static compressive stress concentration around the underground tunnel results in the accumulation of substantial strain energy at the same location the roof and floor of the tunnel are more prone to dynamic failures during the blasting loading process in addition the analysis of energy dissipation indicated that the strain energy reduction and the residual kinetic energy are positively related to the lateral pressure coefficient and the burial depth of the tunnel and the residual kinetic energy is much larger than the strain energy reduction under the same condition furthermore for an underground tunnel subjected to high in situ stress the blasting stress wave with lower amplitude is sufficient to trigger severe dynamic failures

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

accommodating large scale intracontinental extension and compression in a single stress field a key example from the baikal rift system the baikal rift system in southern siberia is one of the main intracontinental extensional features on earth the rift system represents the northwestern boundary of the amuria plate and in that respect can be considered as an evolving plate boundary the baikal rift system has been widely studied both in terms of geology and geophysics and many models have been proposed for its formation and evolution however the age of the initiation of deformation and the mechanism driving this deformation are still largely debated while major extension has occurred since the late miocene pliocene the onset of extension seems older than the india asia collision implying that several driving mechanisms may have acted together or in relay through time in this work we review the available data and models for deformation in an area encompassing the baikal rift system the sayan ranges to the west and the transbaikal to the east using a synthesis of this data and our own field and mapping observations we show that the baikal rift system along with transpressional deformation in the sayan ranges and transtension in the transbaikal area can be explained through major left lateral strike slip systems the deformation is strongly controlled by inherited crustal and lithospheric structures and is distributed over a wide area within the western amuria plate that consequently cannot be considered as a rigid block such distributed deformation is likely to have a strong effect on the structure of the future continental margin if extension evolves towards the formation of oceanic crust

mining induced stress change and consequences of stress path on excavation stability a case study abstract for stability assessments as well as for support design it is important to understand the factors leading to detrimental stress changes stress changes not only influence the demand on the rock support they also change the support capacity of frictional support components such as plain cablebolts stress and stress changes are commonly predicted by numerical models but it is rarely possible to verify these predictions this study presents a practical example illustrating the usefulness of stress change measurements in providing an accurate picture of the mining induced stress changes and their value for numerical model calibration stress changes associated with mining of the 565 6 stope at winston lake mine were measured by four csiro hi stress cells two in the hangingwall and two in the back of a sill drift in order to obtain the full stress history of the hangingwall stresses at the installation time were calculated by use of a three dimensional boundary element program map3d two types of rockmass failure were observed at this mine hangingwall delamination and collapse leading to ore dilution and wedge like failures in the backs of sill drifts all stress cells were located such that they were affected by these failure mechanisms using measured and predicted stress paths this study explains the nature of these two failure modes as experienced at winston lake mine excellent correspondence between measured and predicted stresses is achieved for both the hangingwall and the back of the sill drifts modelled stress rotations in the hangingwall follow closely the stress rotations determined in the field except at the end of the monitoring campaign when the stress cells were affected by inelastic straining of the host rock these measurements assist in understanding the failure processes and in defining the limitations of the adopted numerical models

the tropical madden julian oscillation and the global wind oscillation abstract the global wind oscillation gwo is a subseasonal phenomenon encompassing the tropical madden julian oscillation mjo and midlatitude processes like meridional momentum transports and mountain torques a phase space is defined for the gwo following the approach of wheeler and hendon for the mjo in contrast to the oscillatory behavior of the mjo two red noise processes define the gwo the red noise spectra have variance at periods that bracket 30 60 or 30 80 days which are bands used to define the mjo the correlation between the mjo and gwo is 0 5 and cross spectra show well defined coherent phase relations in similar frequency bands however considerable independent variance exists in the gwo a basic dynamical distinction occurs in the direction of midlatitude wave energy dispersion being predominantly meridional during a mjo and zonal during the gwo this is primarily a winter season feature centered over the pacific ocean a case study during april may 2007 focuses on the gwo and two

subsidence and drowning of a carbonate platform in south central mongolia gobi altai region during the late eifelian to early givetian a synthesis of conodont data magnetic susceptibility and paleoecology abstract new and published stratigraphic data are integrated herein to resolve the age and depositional setting of middle devonian strata in the gobi altai terrane of south central mongolia bayanhongar province the tsagaankhaalga formation emsian eifelian is composed primarily of tabular sandy carbonates it is sharply overlain by dark fine grained volcanoclastic marine sedimentary rock of the govialtai formation givetian which is comparatively unfossiliferous except for sporadic fossiliferous carbonate interbeds the latter unit contains abundant tentaculites as well as a newly recovered collection of conodonts assigned to the lower givetian varcus zone timorensis rhenana or ansatus a positive shift in bulk magnetic susceptibility coincides with the tsagaankhaalga govialtai contact and elevated values within the govialtai correspond to tuffaceous and rhyolitic strata the transition from carbonate facies of the tsagaankhaalga formation to the volcanoclastic shales of the govialtai formation is interpreted as the result of local tectonic activity this may be qualitatively described as a transition from a shallow marine carbonate shoal with an epibenthic fauna tsagaankhaalga to a deeper clastic dominated environment with a nektic fauna govialtai the pulse of tectonism must predate the lower givetian and it echoes the tsakhir event which is recorded by the transition from ordovician silurian carbonates to lochkovian conglomerate these findings provide useful biostratigraphic control and insight into the complex tectonic evolution of the gobi altai terrane and adjacent blocks on the eurasian craton

investigation of fractal distribution law for the trace number of random and grouped fractures in a geological mass a fractal study method of the number of geological mass fractures is introduced in detail in this paper three main aspects of the problem were studied 1 the random distribution of fractures in a geological mass was in good agreement with the fractal law the size scale of the studied geological mass ranged from 2400 m to 1 mm for the length of each side and the geological mass samples were taken from 13 coal areas in china 2 the geological mass fractures were evidently directional and anisotropic having originated from tectonic movement observation and statistics for the data from the xuangang fenxi and dongshan coal areas in shanxi china demonstrated that the fracture distribution of each group classified by the strike of the strata still follow the fractal law even though the fractal dimension varies to a certain extent with different strikes 3 the sedimentary strata containing the coal seams as a geological mass underwent almost similar tectonic movements in their geological history the mechanical experiments on geological mass samples from fenxi and jiexiu in shanxi demonstrated that the fractal dimension of the number of fractures in the same strata is in good power function with the product of strength and elastic modulus the larger the product of the strength of the elastic modulus is the larger is the fractal dimension and vice versa