response of daily and annual shell growth patterns of the intertidal bivalve phacosoma japonicum to holocene coastal climate change in japan abstract it is well known that the latitudinal distribution of shallow marine mollusks around the japanese islands has changed episodically during the holocene in response to climate change however few studies have investigated the biotic response of individual species to holocene climate change at daily to annual scales of temporal resolution holocene shells of the venerid phacosoma japonicum recovered from various sites in japan preserve lunar daily and annual growth increments in the outer shell layer and hinge plate as also observed in modern shells sclerochronological analysis of 29 shells with known 14 c ages revealed that the life history traits e g length of the growth period and the mean lunar daily growth rate at a given age have changed markedly over the past 8000 years the intra annual patterns of lunar daily increments and shell oxygen isotope records of the fossil shells can be compared with those of modern specimens from various locations which are constrained by annual patterns of seawater temperature and summer autumn precipitation rates furthermore the temporal trends recorded in the fossil shells show a strong correlation with climate change in mid latitude parts of east asia over the past 8000 years indicating that p japonicum has changed its life history traits in response to holocene terrestrial and coastal climate change

the western ailaoshan volcanic belts and their se asia connection a new tectonic model for the eastern indochina block the western ailaoshan wal volcanic belts mark the western boundary of the south china indochina suture zone along the ailaoshan fold belt geochronological and geochemical evidence suggests that the wal volcanic belts vary in ages and origins and includes 1 l carboniferous earliest m permian ca 300 270 ma incipient backarc basin magmatism 2 m permian ca 265 ma island arc mature backarc basin magmatism 3 early l permian ca 260 255 ma wal indochina arc continent collision and the associated syn collisional granitic magmatism as well as subsequent 4 e triassic ca 250 245 ma post collisional magmatism regional geological comparison indicates that the post l carboniferous wal tectonic evolution was closely related to the eastern indochina block we present a new g plate geodynamic evolution model for the ailaoshan fold belt and its surrounding south china indochina region based on new and published u pb zircon ages together with whole rock and pb isotope geochemical data

geochronology of the sequence hosting the broken hill pb zn ag orebody australia robust stratigraphic control and constraints on the timing of events have been established for the paleoproterozoic metasedimentary and metavolcanic succession that hosts the broken hill pb zn ag orebody in western new south wales geologically consistent depositional intrusive and metamorphic ages are elucidated by means of shrimp u pb analyses of zircon and integrated field studies comparisons of the new shrimp results with those of previous studies clarify some previously untenable age interpretations a range of zircon provenance ages is found in albitic metasedimentary rocks from one of the oldest recognized parts of the willyama supergroup thackaringa group the zircons indicate maximum depositional ages of 1720 to 1730 ma and a minimum stratigraphic age for the lower thackaringa group is constrained by the 1704 3 ma intrusive alma gneiss the latter is the same age as gneissic granitoid rocks in the redan zone southern broken hill domain 1703 3 1705 3 ma felsic magmatism of this age has long been known in the contiguous olary domain south australia but has not been recognized previously at broken hill depositional ages in the broken hill group the upper part of which hosts the pb zn ag orebody indicate that the entire package was deposited within a period of ca 10 m y an age of 1685 3 ma for felsic metavolcaniclastic rocks in the hores gneiss spatially and stratigraphically associated with the ore horizon corroborates previous work this age is within error of that determined for the hanging wall and footwall unit rasp ridge gneiss of the orebody 1683 3 ma it suggests that felsic magmatism in the rasp ridge gneiss was coeval with that of the hores gneiss previous interpretations which suggested that the hores gneiss is not a single stratigraphic entity but comprises younger intrusions having ages from 1690 to1640 ma are not supported by our data and conclusions the stratigraphic integrity of the broken hill group excluding some mafic intrusions is further supported by results from an older formation near its base where tuffaceous metasedimentary rocks from the ettlewood calc silicate member allendale metasediments define an age of 1693 4 ma this is in good agreement with the age of 1693 5 ma for the immediately overlying parnell formation provenance ages obtained from detrital zircons in broken hill group psammites indicate a remarkable uniformity of paleoproterozoic and late archean source s generally matching provenance ages are found in the overlying sundown group psammopelites suggesting a stable flux of sediment fill as the basin deepened and matured similar provenance is indicated for upper paragon group sedimentary rocks and inherited zircons in most of the younger granitoids have age spectra similar to those of the detrital zircons the perpetuation of these age patterns in both clastic detritus and magmatic xenocrysts thus broadly fingerprints exposed and buried older crustal elements that provided material to produce the willyama supergroup basin fill tuffaceous metasiltstones in the middle paragon group bijerkerno metasediments are interpreted to have been derived partly from air fall volcaniclastic material and give consistent depositional ages of 1655 4 and 1657 4 ma in the northern broken hill and euriowie blocks respectively younger tuffaceous metasiltstones in the upper paragon group dalnit bore metasediments provide a stratigraphically consistent maximum depositional age of 1642 5 ma zircon ages from granitoid intrusions that bracket the deformation events suggest that the d 2 and d 3 deformations are inseparable within the interval 1597 3 to 1591 5 ma low th u zircon overgrowths are ubiquitous and irrespective of stratigraphic position record metamorphic ages of 1600 ma metamorphic rutile has the same age confirming that high grade metamorphic event s and d 2 and d 3 structural events were approximately synchronous we find no isotopic support for any pre 1600 ma high grade metamorphic events using newly acquired local age control for the galena pb isotope growth curve the new data support a stratigraphic syngenetic or diagenetic model of primary ore formation for the broken hill orebody at ca 1690 ma although the present distribution of the lodes likely reflects displacement as a result of later structural remobilization

zircon u pb ages and geochemistry of granitoids in the truong son terrane vietnam tectonic and metallogenic implications abstract truong son terrane one of the most important tectonic and metallogenic terranes in indochina block is composed of many volcano plutonic complexes reported here is geochronological and geochemical data obtained from six different volcano plutonic complexes the new data reveals that the granite from the hai van complex is 438 ma in age and shows collision related geochemical characteristics whereas another five samples from five volcano plutonic complexes present consistent emplacement and crystallization ages ranging from 261 to 242 ma dien bien granodiorite phia bioc monzogranite and dong trau rhyolite display typical subduction related calc alkaline affinity e g depletion in nb ta and ti and enrichment in rb and la while monzogranite from song ma complex displays collision related shoshoniteseries and granites from bengiang queson complex are related to post collision calc alkaline series based on these observations in combination with the previous published geochronological data we propose that at least four major stages of magmatic activities occurred during the paleozoic and the early mesozoic through the truong son terrane ordovician silurian 420 470 ma late carboniferous early permian 280 300 ma late permian to mid triassic 245 270 ma and middle late triassic 200 245 ma these magmatic activities are not only attributed to the tethyan song ma ocean southwestward subduction but also related to paleo tamky phuoc son oceanic bidirectional subduction synthesized with regional metallogenic data we identified three metallogenic epochs 1 late carboniferous early permian 280 300 ma arc magmatic hydrothermal cu au fe polymetallic metallogenic system related to the tamky phuoc son ocean north dipping subduction 2 late permian middle triassic 245 280 ma arc magmatic hydrothermal cu au fe and orogenic w sn au polymetallic metallogenic system which linked to both paleo tethyan song ma ocean south dipping subduction and tamky phuoc son ocean closure 3 middle to late triassic 200 245 ma syn collisional magmatic epithermal fe au w sn and post collisional or orogenic au system

understanding kinematic data from the moine thrust zone in terms of a kinematics based mathematical model of deforming thrust wedges abstract a salient recess pair along the moine thrust zone exhibits significant lateral kinematic variations specifically the more steeply dipping portion of the thrust surface associated with the recess shows evidence for greater strain magnitudes and more out of the plane motion than the adjoining salient additionally a subset of the grain shape data has grain shape approximations with their long axes oriented perpendicular to the regional transport direction to more fully understand these kinematic features we developed a kinematics based mathematical model of thrust wedge deformation our numerical model predicts an increase in strain magnitude as well as non plane strain flattening in the region of a thrust ramp consistent with the strain patterns observed within the recess along the moine thrust zone furthermore in the absence of a lateral confining boundary condition much of the model thrust wedge experiences transport perpendicular maximum extension except for the region closest to the thrust where simple shear deformation is dominant using our numerical model we predict the amount of lateral confining strain needed to induce plane strain deformation ps as well as the amount of lateral confining strain necessary to make the long axis of the strain ellipsoid parallel with the transport direction parallel we have found that the incremental parallel can be as much as 42 of the incremental strain magnitude thus we consider transport perpendicular lineations like those seen along the moine thrust zone to be the result of lateral confining boundary conditions that are weak enough to allow transport perpendicular maximum extension

clustering and stress inversion in the song tranh 2 reservoir vietnam the seismicity in the vicinity of the song tranh 2 reservoir that commenced in late 2010 is an example of reservoir induced seismicity moment tensor mt solutions are mostly normal faulting mechanisms with shearing as the main component of full mt which suggest reservoir exploitation stress field changes as a triggering origin of this seismicity however the local tectonic stress field plays a role in the seismogenic process which is accelerated by the reservoir exploitation two main orientations of discontinuities reactivated by reservoir exploitation are identified with clustering of events located in two main areas northern and southern in addition to the northern cluster nc and southern cluster sc further smaller clusters are distinguishable assuming both clustering of epicenters and similarity of focal mechanisms as the clustering criteria maximum seismic activities in clusters appear in different periods with high seismicity in the sc preceding that in the nc the results indicate significant differences between the nc and sc it is shown that the sc is an example of rapid triggering whereas the nc is a delayed triggering type also magnitude distribution differs between the nc b 1 1b 1 1 and sc b 1 3b 1 3

silurian radiolarians from the sepon mine truong son terrane central laos and their palaeogeographic and tectonic significance a silurian radiolarian fauna based on 18 species is described from cherts from three sections in two quarries in the sepon mine area central laos each section contains distinctive assemblages but futobari morishitai f solidus zadrappolus yoshikiensis and z tenuis are found in all three sections and are characteristic of the ludlow pridoli z yoshikiensis assemblage in addition the hoei yang pit section contains zadrappolus hitoeganensis pseudospongoprunum sagittatum futobari sp and secuicollacta sp section cq contains pseudospongoprunum sagittatum p tazukawaensis praespongocoelia parva p sp rotasphaera sp cf r quadrata secuicollacta sp cf cassa section qm also contains pseudospongoprunum parvispina p sp zadrappolus sp and devoniglansus seponensis new species thassanapak is common evidence from silurian and devonian strata of the southern truong son terrane indicates deepening towards the southern margin as defined by the thakhek danang shear zone and exemplified by deep marine ludlow pridoli radiolarian cherts in the south shallowing to fossiliferous shallow water sediments to widespread old red sandstone type terrestrial facies 85 km further ne the radiolarian cherts are in faulted contact with probable llandovery limestone and upper ordovician llandovery graptolitic shales the graptolitic shales are overlain with slight angular unconformity by the submarine fan volcaniclastic dominated namphuc formation of llandovery age this fan received andesitic materials from the nearby long dai volcanic arc which extends eastwards to the tamky suture in vietnam this plutonic volcanic arc was probably maintained by northwards subduction along the trend of the permian recent thakhek danang shear zone

neoproterozoic to early triassic tectono stratigraphic evolution of indochina and adjacent areas a review with new data the neoproterozoic to early triassic tectono stratigraphic evolution of indochina and adjacent areas can be divided into six mega episodes 1 the neoproterozoic early cambrian mega episode was characterized by shallow marine environment in the sino vietnam composite terrane meanwhile the different blocks of the indochina composite terranes were still separated by branches of the proto tethys sino vietnam and part of indochina amalgamated along the proto song ma suture by the end of the early cambrian 2 during the middle cambrian early ordovician mega episode shallow shelf carbonate deposition prevailed north of the proto song ma suture with associated strata containing a rich benthic fauna this contrasts with deep marine and volcanic arc setting in the south of the proto song ma suture 3 the middle ordovician silurian mega episode was characterized by subduction of the tam ky phuoc son ocean beneath the viet lao terrane in the north and the kon tum terrane in the south this was followed by a collisional orogeny that sutured the kon tum terrane with the viet lao and viet cambodia terranes along the tam ky phuoc son suture the hypothetic po ko and chu sinh sutures are discussed the collision led to an intra continental orogeny in the sino vietnam composite terrane by the end of the mega episode a unified sino vietnam indochina super terrane was established during the latest silurian early devonian benthic fauna and flora of the sino vietnam and indochina composite terranes shared cathaysian affinity 4 the devonian tournaisian mega episode was characterized by an early middle devonian transgression and a late devonian earliest carboniferous regression except for parts of northern indochina where deep marine conditions remained 5 during the visean middle permian the song ma ocean reopenned in the north of indochina meanwhile in the west a volcano plutonic belt formed due to eastward subduction of the paleo tethys under the indochina composite terrane 6 the late permian early triassic mega episode was characterized by emeishan mantle plume related continental rifting and the indosinian orogeny resulting from resuturing of the indochina and sino vietnam composite terranes along the song ma suture

where was the ailaoshan ocean and when did it open a perspective based on detrital zircon u pb age and hf isotope evidence abstract the indochina simao and yangtze blocks were separated by a branch of the paleo tethys ocean commonly referred as the ailaoshan ocean in the paleozoic remnants of this ailaoshan ocean have been variably suggested to locate along from east to west the ailaoshan fault jiujia anding fault and amojiang lixianjiang fault in order to test these models we have carried out comprehensive detrital zircon u pb dating and hf isotope analyses on the cambrian to devonian sedimentary units in the ailaoshan belt and its adjacent western margin of the yangtze block our results indicate marked detrital zircon provenance variation on different sides of the ailaoshan tengtiaohe fault detrital zircons from east of the fault display a diagnostic age peak at 730 900 ma which is characterized by both positive and negative e hf t values with a hf model age t dm c peak at 1 8 ga whereas detrital zircons from west of the fault display two major age populations of 400 500 and 900 1000 ma both characterized by mainly negative e hf t values with a hf model age t dm c peak at 2 1 ga our new data indicate that detritus from east and west of the ailaoshan tengtiaohe fault may have been mainly derived from respectively the yangtze block and indochina simao blocks thus suggesting the fault may represent the actual suture between the two blocks our study also reveals that the ailaoshan ocean may have started its early continental rift in the early silurian

understanding mesozoic accretion in southeast asia significance of triassic thermotectonism indosinian orogeny in vietnam results from a zircon u pb study of the metamorphic basement of vietnam reveal that a large part of the continental crust was affected by a short lived episode of ductile deformation and high temperature metamorphism between 258 6 ma and 243 5 ma although coincident with final stages of north south china collision qinling orogenesis the thermotectonism in vietnam was caused by accretion of sibumasu to indochina south china this accretion event indosinian orogeny has regional significance because it contributed to the final stages of north south china collision an aspect not explicitly recognized in qinling orogenic models

large variations in holocene solar activity constraints from 10be in the greenland ice core project ice core 1 cosmogenic radionuclides extracted from ice cores hold a unique potential for reconstructing past solar activity changes beyond the direct instrumental period taking the geomagnetic modulation into account the solar activity in terms of the heliospheric modulation function can quantitatively be reconstructed in high resolution throughout the holocene for this period our results reveal changes in heliospheric modulation of galactic cosmic rays significantly larger than the variations reconstructed on the basis of neutron monitor measurements of galactic cosmic rays for the last 50 years moreover the 10be data from the greenland ice core project ice core as well as 14c support a high current solar activity however although the reconstruction of solar activity on long timescales is difficult our result suggests that the modern activity state of the sun is not that exceptional regarding the entire holocene this extended solar activity record provides the basis for further detailed investigations on solar and cosmic ray physics as well as on solar forcing of the earth s climate whose importance is suggested by increasing paleoclimatic evidences

explosive volcanic eruptions triggered by cosmic rays volcano as a bubble chamber abstract volcanoes with silica rich and highly viscous magma tend to produce violent explosive eruptions that result in disasters in local communities and that strongly affect the global environment we examined the timing of 11 eruptive events that produced silica rich magma from four volcanoes in japan mt fuji mt usu myojin sho and satsuma iwo jima over the past 306 years from ad 1700 to ad 2005 nine of the 11 events occurred during inactive phases of solar magnetic activity solar minimum which is well indexed by the group sunspot number this strong association between eruption timing and the solar minimum is statistically significant to a confidence level of 96 7 this relationship is not observed for eruptions from volcanoes with relatively silica poor magma such as izu ohshima it is well known that the cosmic ray flux is negatively correlated with solar magnetic activity as the strong magnetic field in the solar wind repels charged particles such as galactic cosmic rays that originate from outside of the solar system the strong negative correlation observed between the timing of silica rich eruptions and solar activity can be explained by variations in cosmic ray flux arising from solar modulation because silica rich magma has relatively high surface tension 0 1 nm 1 the homogeneous nucleation rate is so low that such magma exists in a highly supersaturated state without considerable exsolution even when located relatively close to the surface within the penetration range of cosmic ray muons 1 10 gev these muons can contribute to nucleation in supersaturated magma as documented by many authors studying a bubble chamber via ionization loss this radiation induced nucleation can lead to the pre eruptive exsolution of h 2 o in the silica rich magma we note the possibility that the 1991 mt pinatubo eruption was triggered by the same mechanism an increase in cosmic ray flux triggered by typhoon yunya as a decrease in atmospheric pressure results in an increase in cosmic ray flux we also speculate that the snowball earth event was triggered by successive large scale volcanic eruptions triggered by increased cosmic ray flux due to nearby supernova explosions

an intercalibration study of the fish canyon sanidine and biotite 40ar 39ar standards and some comments on the age of the fish canyon tuff the age of the fish canyon tuff fct has been the subject of intense study due to its potential significance as a geochronological test to establish age concordance between the k ar and u pb isotopic systems minerals from the fct notably sanidine and biotite are in widespread use as 40ar 39ar fluence monitors standards and have been employed as both primary and intercalibrated standards in attempting to constrain the true age of fct the distinction between primary vs intercalibrated ages is important as only the primary age determinations are valid an investigation of both fish canyon sanidine fcs and fish canyon biotite fct 3 was undertaken to assess the chemical and isotopic homogeneity of the minerals on a grain to grain scale electron microprobe results show that fcs is chemically homogeneous verifying previous studies although there are some very small zones of minor k depletion fct 3 biotite commonly contains numerous and small mineral inclusions 40ar 39ar experiments further show that fcs is remarkably homogeneous confirming previous observations whereas fct 3 shows much greater isotopic variability due to contamination from the mineral inclusions by setting the age of fcs equal to 27 98 0 15 ma 2 as intercalibrated to the u pb system by villeneuve et al 2000 the resultant intercalibration factor between fcs and fct 3 is 1 005 0 017 yielding an age of 28 13 0 47 ma 2 for fct 3 although the significant intragrain chemical and isotopic variability precludes its use as an effective 40ar 39ar fluence monitor the true age of the fct is problematic a survey of all primary ages for fct shows that mean k ar ages for plagioclase hornblende biotite and sanidine are consistently younger than mean u pb ages from titanite and zircon in conjunction with recently published petrological results which indicate that the fct contains material from multiple crystallization events this significant discrepancy between the k ar and u pb data sets demonstrates that the fish canyon tuff cannot serve as a golden standard between the k ar and u pb systems

temperature trends over the past five centuries reconstructed from borehole temperatures for an accurate assessment of the relative roles of natural variability and anthropogenic influence in the earth s climate reconstructions of past temperatures from the pre industrial as well as the industrial period are essential but instrumental records are typically available for no more than the past 150 years therefore reconstructions of pre industrial climate rely principally on traditional climate proxy records each with particular strengths and limitations in representing climatic variability subsurface temperatures comprise an independent archive of past surface temperature changes that is complementary to both the instrumental record and the climate proxies here we use present day temperatures in 616 boreholes from all continents except antarctica to reconstruct century long trends in temperatures over the past 500 years at global hemispheric and continental scales the results confirm the unusual warming of the twentieth century revealed by the instrumental record but suggest that the cumulative change over the past five centuries amounts to about 1 k exceeding recent estimates from conventional climate proxies the strength of temperature reconstructions from boreholes lies in the detection of long term trends complementary to conventional climate proxies but to obtain a complete picture of past warming the differences between the approaches need to be investigated in detail

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

possible link between multi decadal climate cycles and periodic reversals of solar magnetic field polarity abstract the linkage between multi decadal climate variability and activity of the sun has been long debated based upon observational evidence from a large number of instrumental and proxy records it is difficult to evaluate the exact role of each of solar parameters on climate change since instrumentally measured solar related parameters such as total solar irradiance tsi ultra violet uv solar wind and galactic cosmic rays gcrs fluxes are more or less synchronized and only extend back for several decades here we report tree ring carbon 14 based record of 11 year 22 year solar cycles during the maunder minimum 17th century and the early medieval maximum period 9 10th century to reconstruct the state of the sun and the flux of incoming gcrs the result strongly indicates that the influence of solar cycles on climate is persistent beyond the period after instrumental observations were initiated we find that the actual lengths of solar cycles vary depending on the status of long term solar activity and that periodicity of the surface air temperatures are also changing synchronously temperature variations over the 22 year cycles seem in general to be more significant than those associated with the 11 year cycles and in particular around the grand solar minima such as the maunder minimum 1645 1715 ad the polarity dependence of cooling events found in this study suggests that the gcrs can not be excluded from the possible drivers of decadal to multi decadal climate change

nao signal recorded in the stable isotopes of greenland ice cores 1 the winter 18o signal is extracted from 7 greenland ice cores covering the past 700 years to filter out noise and local variations in the 7 isotope records a principal component analysis is carried out on the ice core data a comparison between the time series of the first principal component pc1 with 67 years of winter december to march temperature measurements from 3 southern greenland synoptic stations shows highly significant correlations southern greenland winter temperatures are known to be greatly influenced by the north atlantic oscillation nao a good proxy for southern greenland temperatures is therefore expected to reveal at least parts of the nao signal it is shown that the pc1 time series indeed is significantly correlated to the nao during the winter months the inclusion of ice core winter season 18o time series in future multiproxy nao reconstructions is therefore recommended

reply to the comments by alsop and holdsworth on evidence for non plane strain flattening along the moine thrust loch strath nan aisinnin north west scotland

early paleozoic or early middle triassic collision between the south china and indochina blocks the controversy resolved structural insights from the kon tum massif central vietnam abstract in central vietnam the kontum massif is subdivided from north to south into i kham duc ii ngoc linh iii kan nack complexes the kham duc complex consists of metapelite metapsammite paragneiss metagabbro amphibolite serpentinized ultramafic and orthogneiss blocks the southern part of this complex experienced an early paleozoic crustal melting event responsible for migmatites and anatectic granites the ngoc linh complex the largest one is formed by metatexite and granitoid enclosing blocks of eclogite high pressure hp granulite orthogneiss metagabbro amphibolite granodiorite and migmatite the kan nack complex is formed by migmatites with ultra high temperature u ht granulite charnockites and enderbites the three metamorphic complexes are intruded by per aluminous granite and subordinate mafic plutons in spite of local variations the foliation of the ngoc linh complex defines a bulk domal structure and the stretching lineation consistently trends nw se the nw se lineation is also observed in the tectonically overlying the kan nack complex the ngoc linh and kan nack complexes are interpreted here as parts of a metamorphic core complex mcc or ngoc linh mcc exhumed by a top to the nw detachment fault along the northern margin of the ngoc linh mcc upright folds with e w striking axes and e w stretching lineation deform the foliation these structures are developed in a transpressive regime coeval with the activity of plurikilometer scale dextral strike slip faults zircon and monazite u pb radiometric datings document a 250 240 ma age for the crustal melting and the top to the nw ductile shearing coeval with the formation of the ngoc linh mcc this extensional tectonics is followed by a dextral strike slip faulting at ca 240 230 ma before the emplacement of the two mica granitic plutons at ca 240 224 ma furthermore in the ngoc linh and kan nack complexes zircon and monazite yield u pb early paleozoic ages in the kham duc complex a ca 460 ma mp mt garnet biotite staurolite kyanite metamorphism followed by migmatites at ca 450 ma is also recognized the 420 400 ma age of the dai loc plutonic suite and the 450 425 ma age of the dien binh calc alkaline granodiorite document an early paleozoic event the early paleozoic mafic and ultramafic masses of the hiep duc complex are ophiolites included into a metasedimentary matrix thus the kham duc complex is interpreted as a tectonic melange formed during a collisional orogeny that subsequently underwent crustal melting giving rise to the migmatites a part of the early paleozoic rocks are enclosed as xenoliths in the triassic migmatite of the ngoc linh mcc these petrologic structural and chronological features allow us to propose the following geodynamic evolution for the kontum massif during the early paleozoic a continental collision which was accommodated by a north directed subduction of a southern block s vietnam or viet cambodia block below a northern block n vietnam or viet lao block occurred along the tam ky phuoc son suture during the early triassic at ca 250 245 ma the s vietnam block experienced a crustal melting giving rise to the ngoc linh mcc that reworked the early paleozoic orogen lastly during the middle triassic the dextral faulting superimposed upon the ngoc linh migmatite the geodynamic significance of the kontum massif is discussed in the general framework of indochina south china relationships the early paleozoic collision in vietnam is viewed as the driving force responsible for the development of the intracontinental orogeny of s china in order to account for the important heat flow required for the formation of uht metamorphic rocks a possible interaction between the scb indochina collision and the emeishan mantle plume is proposed

carboniferous triassic felsic igneous rocks and typical mineral deposits in the truong son orogenic belt se asia implications for paleo tethyan tectonic evolution and metallogeny abstract the truong son orogenic belt tsob is part of the eastern tethyan mineral deposit domain and preserves a near complete record of paleo tethyan orogeny related magmatism and mineralization by compiling and evaluating the data of plutonic and sub volcanic rocks and associated deposits on a regional scale and combining with new data of typical igneous rocks and mineral deposits we establish a unified paleo tethyan evolutionary model to help understanding the metallogeny in the tsob the geochronological data reveal the felsic magmatism and associated mineralization occurred in carboniferous triassic ca 317 202 ma with a magmatic lull at ca 270 263 ma before the lull most igneous rocks are high mg sodic metaluminous i type granitoids or volcanic equivalents with depleted hf isotopes which were derived from a juvenile crustal source with significant mantle contribution after the lull the igneous rocks ca 262 235 ma consist of metaluminous i type granitoids and abundant s type granitoids with geochemical features of low mg potassic peraluminous and enriched hf isotopes suggesting their derivation from ancient continental crust without obvious mantle contribution this magmatic lull corresponds to the tectonic transition from subduction to initial collision which reasonably accounts for the changing of petrogenetic types and magma sources of the associated igneous rocks in the tsob the slightly depleted hf isotopes of the ca 234 202 ma rocks possibly suggest another episode of tectonic transition in late triassic the distinct mineralization styles and s isotopes of ore deposits of each episode indicate that mineralization was related to the tectonic evolution and magmatism in each stage here we propose an evolutionary model for the paleo tethys orogeny in the tsob as follows 1 low angle subduction beneath the tsob during late carboniferous late permian favored the formation of juvenile crust derived adakitic rocks and high mg i type felsic rocks as well as associated porphyry cu au skarn fe cu au and epithermal au ag mineralization 2 subsequent collision during late permian middle triassic not only accounted for the generation of precambrian crust derived i type granitoids and intrusion related au ag deposits but also resulted in the formation of low mg s type rocks minor volcanic rocks and associated porphyry and or skarn sn zn pb deposits 3 possible post collisional extension during late triassic may be favorable for the formation of metaluminous high k high mg i type granitoids and volcanic rocks and carlin au porphyry and or skarn mineralization

tectonics and metallogeny of mainland southeast asia a review and contribution abstract the southeast asia region is endowed with a diversity of mineral resources notably porphyry related skarn epithermal and sediment hosted orogenic gold deposits formation of these deposits was associated with a long and complex tectonic history of gondwana supercontinent break up arc magmatism backarc basin development together with arc continent and continent continent collisions that created the present day mainland se asia this paper summarizes historical and current se asian geological research and ore deposit studies here we present a new tectonic and metallogenic model for phanerozoic mainland se asia from this model we conclude that incipient arc backarc basin magmatism is the key to the formation of many important ore deposits in the truong son and loei fold belts the two major metallogenic belts in mainland se asia in addition triassic to cenozoic arc continent and continent continent collisions have led to the formation of many sediment hosted orogenic gold deposits in the sukhothai and the sibumasu terranes oblique cretaceous to recent subduction along the andaman sunda trench was responsible for gold and copper gold molybdenum porphyry and epithermal mineralization along the kawlin wutho mt popa arc in myanmar in the north and the sumatran volcanic arc in the south we anticipate that the present emphasis on exploring for shallower level epithermal deposits will increasingly lead to exploration for deeper level porphyry and porphyry related skarn systems in the coming decades

geodynamics of the indosinian orogeny between the south china and indochina blocks insights from latest permian triassic granitoids and numerical modeling

temporal and three dimensional spatial analyses of the frequency magnitude distribution near long valley caldera california summary the 3 d distribution of the b value of the frequency magnitude distribution is analysed in the seismically active parts of the crust near long valley caldera california the seismicity is sampled in spherical volumes containing n 150 earthquakes and centred at nodes of a grid separated by 0 3 km significant variations in the b value are detected with b ranging from b 0 6 to b 2 0 high b value volumes are located near the resurgent dome and at depths below 5 km at mammoth mountain b values are found to be much lower south of the long valley caldera we interpret this to indicate that an active magma body has advanced from depths below 8 km to depths of 4 to 5 km beneath mammoth mountain in 1989 and that anomalous crust either highly fractured or containing unusually high pore pressure such as is the case in the vicinity of active magma bodies exists north of the seismically active area beneath the resurgent dome at all depths we also investigate the spatial distribution of temporal variations of the frequency magnitude distribution by introducing diverential b value maps b values increased from b 0 8 to b 1 5 underneath mammoth mountain at the onset of the 1989 earthquake swarm and remained high thereafter this suggests that an intrusion permanently altered the average distribution of cracks at 5 10 km depth or that the pore pressure permanently increased we propose that high b values are a necessary but not suycient condition near a magmatic body and therefore spatial b value mapping can be used to aid in the identification of active magma bodies

40ar 39ar geochronology of the charnockites and granulites of the kan nack complex kon tum massif vietnam abstract the truong son belt forms the eastern rim of the indochina block in southeast asia the age of the metamorphism mainly along nw se mylonitic shear zones that affects this belt has been formerly determined at about 240 250 ma this age corresponds to the indosinian tectonometamorphic episode the kon tum massif situated to the south of this belt comprises high temperature rocks the kan nack complex including charnockites and granulites the main charnockitic outcrops restricted to the song ba valley establish the intrusive nature of these magmatic rocks within granulite facies material basic charnockitic rocks are mainly quartz enderbites to norites and hornblende pyroxene granulite facies rocks the 40 ar 39 ar age of intrusion cooling of charnockitic magmas is determined from primary magmatic biotites at about 245 ma in the east of the kan nack complex some granulite facies rocks exhibit relicts of primary granulite facies parageneses whereas others show evidence of overprinting by a retrogressive low grade metamorphism ar ar dating confirm this evolution giving ages of 400 ma for primary relict granulite facies phases and 260 270 ma from the most retrogressed samples establishing the youngest limit for the granulite facies metamorphism granulites intruded by charnockites in the song ba valley yield ages of about 250 ma equivalent to the ages of the charnockites and have evidently been completely reset by these high temperature intrusions therefore the kan nack complex of the kon tum massif is not an independent unit with respect to the indosinian orogen but represents the deep crustal part of this belt

climatic and environmental changes at southeastern coast of lake biwa over past 3000 years inferred from borehole temperature data abstract in order to infer past climatic change in central japan we measured temperatures in a borehole at the karasuma site on the southeastern coast of lake biwa and reconstructed sediment surface temperature history during the last 3000 years the reconstructed temperature history shows apparent medieval warm period little ice age and contemporary temperature warming however the large amplitude of the temperature changes up to 4 5 k cannot be explained by past climatic change only suggesting that there was some other cause of the larger amplitude temperature changes the onsets of temperature decrease in the late 12th century a d and temperature increase in the mid 17th century a d appear to coincide with occurrences of two destructive earthquakes 1185 and 1662 a d that caused water level changes of lake biwa it suggests that the reconstructed sediment surface temperature history reflects the environmental change due to tectonically induced water level changes of the lake if the annual mean of the ground surface temperature was higher than that of the bottom water temperature in a shallow part of the lake which is consistent with the present day data the large amplitude of the sediment surface temperature change may be attributed to a combined effect of past climatic and environmental changes thus we suggest that the borehole temperature at the karasuma site preserves information not only on past climate changes but also on environmental changes due to tectonically induced water level changes

the endogenetic metallogeny of northern laos and its relation to the intermediate felsic magmatism at different stages of the paleotethyan tectonics a review and synthesis abstract northern laos is at the junction of the paleo tethys convergence and assemblages of several crustal blocks such as the sibumasu south china and the indochina blocks and also comprises the houayxay sukhothai the simao phongsaly the louang phrabang loei the truong son and the song da terranes during the amalgamation of the terranes derived from gondwana calc alkaline magmatic rocks peraluminous magmatic rocks sub alkaline volcanic intrusive complexes and alkaline rocks and related endogenetic metallogenic systems were emplaced in multiple stages during subduction collision and post collision events according to chronological order the tectonic magmatic development processes and the metallogenic assemblages can be divided as follows 1 subduction arc related magmatic hydrothermal metallogenic systems formed in calc alkaline magmatic rocks due to the initial subduction during the late carboniferous including porphyry cu au deposits skarn and epithermal cu au deposits 2 arc continent collisions and back arc extensional settings and associated magmatic hydrothermal mineralization with calc alkaline porphyry cu au deposits as well as alkaline porphyry and epithermal cu au deposits during the early permian 3 collisional orogenic magmatic hydrothermal metallogenic systems formed in the late permian to the early to middle triassic comprising high alumina magmatic rocks with au pb zn ag fe cu deposits associated with both orogenic type and hydrothermal vein type and 4 post orogenic extensional tectonic hydrothermal metallogenic assemblages which were formed in calc alkaline to alkaline rocks within a extensional tectonic setting during the late triassic early jurassic including porphyry cu mo sn deposits porphyry skarn and epithermal cu au deposits and also subalkaline volcanic intrusive complex related hydrothermal stratabound cu pb zn and au sb hg deposits further detailed studies and classification of metallogenic assemblages in laos is of significance to understand the nature and timing of different mineralization styles in relation the evolution of the paleo tethys

anomalous mesozoic thermal regime central appalachian piedmont evidence from sphene and zircon fission track dating a total of 17 sphene and 45 zircon fission track ages fta are reported from the piedmont province of pennsylvania delaware and maryland the reading prong of new jersey and the newark basin of pennsylvania with the exception of one sphene sample fta fall within a relatively restricted age range sphene 190 217 ma average 199 ma and zircon 143 218 ma average 184 ma near concordance of fta over a large tract of crystalline basement sim20 000 km 2 and within upper triassic sediments in the newark basin indicates late triassic early jurassic total resetting of the fission track clocks followed by regional cooling between sphene sim275 pm 25 circ c to zircon sim 220 pm 40 circ c closure temperatures at rates of 4 8 c ma fourteen rb sr whole rock mica ages together with previously reported 40 ar 39 ar biotite and hornblende ages generally indicate no regional mesozoic resetting thus the maximum temperature experienced by the samples was 300 c sphene fta clo

full moment tensor inversion as a practical tool in case of discrimination of tectonic and anthropogenic seismicity in poland tectonic seismicity in poland is sparse the biggest event was located near my lenice in 17th century of magnitude 5 6 on the other hand the anthropogenic seismicity is one of the highest in europe related for example to underground mining in upper silesian coal basin uscb and legnica glogow copper district lgcd open pit mining in belchatow brown coal mine and reservoir impoundment of czorsztyn artificial lake the level of seismic activity in these areas varies from tens to thousands of events per year focal mechanism and full moment tensor mt decomposition allow for deeper understanding of the seismogenic process leading to tectonic induced and triggered seismic events the non dc components of moment tensors are considered as an indicator of the induced seismicity in this work the mt inversion and decomposition is proved to be a robust tool for unveiling collapse type events as well as the other induced events in polish underground mining areas the robustness and limitations of the presented method is exemplified by synthetic tests and by analyzing weak tectonic earthquakes the spurious non dc components of full mt solutions due to the noise and poor focal coverage are discussed the results of the mt inversions of the human related and tectonic earthquakes from poland indicate this method as a useful part of the tectonic and anthropogenic seismicity discrimination workflow

detailed analysis of acoustic emission activity during catastrophic fracture of faults in rock abstract the detailed time space distribution of acoustic emission ae events during the catastrophic fracture of rock samples containing a pre existing joint or potential fracture plane is obtained under triaxial compression using a high speed 32 channel waveform recording system and the results are discussed with respect to the prediction and characterization of catastrophic fault failure ae activity is modeled quantitatively in terms of the seismic b value of the magnitude frequency relation the self excitation strength of the ae time series and the fractal dimension of ae hypocenters consistent with previous studies on rock samples containing a fracture plane with several asperities the present analyses reveal three long term phases of ae activity associated with damage creation on heterogeneous faults each clearly identifiable based on the above parameters a long term decreasing trend and short term fluctuation of the b value in the phase immediately preceding dynamic fracture are identified as characteristic features of the failure of heterogeneous faults based on the experimental results it is suggested that precursory anomalies related to earthquakes and other events associated with rock failure are strongly dependent on the heterogeneity of the fault or rock mass a homogeneous fault or rock mass appears to fracture unpredictably without a consistent trend in precursory statistics while inhomogeneous faults fracture with clear precursors related to the nature of the heterogeneity

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

fish suggests continental connections between the indochina and south china blocks in middle devonian time a yunnanolepiform antiarch placoderm fish is recorded from the givetian dong tho formation of quang binh province central vietnam this and other fishes from the same locality occur in marginal marine detrital facies with plant remains and lingulid brachiopods that indicate a nearshore to deltaic environment yunnanolepiform antiarchs were hitherto known exclusively from the lower devonian of the south china block the new occurrence of this group well south of the song ma suture suggests close links between the indochina and south china blocks in middle devonian time the massive sandstone exposures of the dong tho formation may be a southern extension of the do son sandstone formation of the hai phong area which is located on the south china block

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

finite strain and strain variation analysis in the sheeprock thrust sheet an internal thrust sheet in the provo salient of the sevier fold and thrust belt central utah abstract the sheeprock thrust sheet in west central utah is an internal thrust sheet in the provo salient of the sevier fold and thrust belt we have measured finite strain in quartzites the dominant lithology sampled along a square grid within the thrust sheet using the modified normalized fry method mcnaught m a 1994 modifying the normalized fry method for aggregates of non elliptical grains journal of structural geology16 493 503 the x y and x z axial ratios from unsampled locations within the sample area were estimated using the spatial statistics approach the strain ellipsoids exhibit a variable three dimensional orientation pattern resulting from modification of the initial layer parallel shortening lps strain ellipsoid by fault parallel shear in conjunction with vertical flattening and or horizontal stretching indicating that the thrust sheet did not undergo plane strain deformation in the transport plane this suggests that the plane strain assumption used in drawing restorable balanced cross sections breaks down for internal thrust sheets with more than one penetrative strain producing deformation event the x z strain axial ratios decrease away from the thrust towards the middle of the sheet the x y strain axial ratios from interpolated image diagrams indicate transport parallel stretching at the front end of the sheet and strike parallel stretching at the back end of the sheet the footwall and hanging wall finite strain patterns are similar indicating that most of the strain in the sheeprock thrust sheet developed early in the deformation history of the thrust sheet before and perhaps during the growth of a large fault propagation fold pair

multistage sedimentary and metamorphic origin of pyrite and gold in the giant sukhoi log deposit lena gold province russia gold mineralization at sukhoi log in eastern siberia is hosted in a deformed neoproterozoic organic bearing and pyritic black shale and siltstone sequence that is folded into a tight overturned anticline the deposit contains about 30 million ounces of gold at an average grade of 2 0 g t au and is one of the largest known undeveloped gold resources the high grade gold zone forms a gently dipping tabular body in the core of the anticline the best gold grades occur in narrow bedding parallel pyrite quartz veinlets that have been folded during the main deformation event lower grade gold is associated with disseminated pyrite developed in and around the high grade core of the deposit detailed paragenetic studies of the mineralization and host rocks have defined six stages of pyrite development in the carbonaceous sediments the two earliest forms of pyrite termed py1 and py2 are commonly developed in stratiform layers of micron sized crystals framboids and fine euhedra which are interpreted as synsedimentary to early diagenetic in origin coarser grained bedding parallel aggregates of inclusion rich pyrite termed py3 contain inclusions of arsenopyrite native gold and gold tellurides and are interpreted to form during late diagenesis and earliest deformation coarse euhedral pyrite py4 overgrows the earlier pyrite py1 py2 and py3 and the slaty cleavage developed in the host rocks indicating a syndeformation timing late stage inclusion free pyrite py5 overgrows and replaces earlier sulfides and is considered to be syn to late deformation laser ablation inductively coupled plasma mass spectrometry la icpms analyses of the various pyrite types indicate that the synsedimentary py1 contains the highest levels of invisible gold varying from 0 4 to 12 1 ppm with a mean of 3 22 ppm au and 1 900 ppm as py1 is also enriched in a suite of trace elements mo sb ni co se te ag cu pb zn mn ba cr u v which are similar to those concentrated by organic processes in euxinic sedimentary environments later generations of pyrite from py2 to py5 including pyrite in bedding parallel pyrite quartz veinlets contain progressively lower contents of invisible gold and most other trace elements however this metamorphic and postmetamorphic pyrite contains microinclusions of free gold arsenopyrite pyrrhotite sphalerite and chalcopyrite the paragenetic textural and chemical relationships at sukhoi log suggest that gold was clearly initially introduced prior to cleavage development accompanying sedimentation of the organic rich shales and fixed during diagenesis within the structure of diagenetic arsenian pyrite subsequently accompanying deformation gold was liberated from recrystallized diagenetic pyrite to become concentrated as free gold and gold tellurides within metamorphic pyrite and folded bedding parallel pyrite quartz veinlets two key processes are considered vital to the formation of the sukhoi log deposit original synsedimentary and early diagenetic concentration of gold dissolved within arsenian pyrite in organic rich black shales and metamorphic processes that liberated gold from the early forms of arsenian pyrite to be concentrated as free gold and gold tellurides within late diagenetic and metamorphic pyrite and associated pyrite quartz veinlets in the core of an overturned anticline these ore forming processes are unlikely to be unique to sukhoi log other black shale and turbidite hosted deposits that occur in rifted continental margin environments which have undergone collision and basin inversion may form by similar processes

complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones abstract many of the complex strain patterns seen in shear zones and thrust zones such as variable fabric orientations refolded folds and fabrics together with folds with hinges almost parallel to the main transport direction can be explained in terms of differential movement within the shear zones these strains are developed at the frontal and lateral tips of the zones as they propagate examples are taken from the moine thrust zone of scotland which show variations in strains particularly at the lateral tips the form of differential movement described here may lead to complex strain paths and non plane strain ellipsoids and the spatial variations in finite strain may be used to delineate zones of extensional and compressional flow and differential movement in the shear zones or thrusts

indosinian nw trending shear zones within the truong son belt vietnam 40ar39ar triassic ages and cretaceous to cenozoic overprints abstract several nw trending ductile and partly mylonitic shear zones cross the truong son belt of central vietnam along the song ma and song ca valleys and north of the kontum block from da nang to aluoi and khe sanh high grade metamorphic rocks of amphibolite facies showing a retrograde evolution and consisting of ortho and paragneisses metavolcanics amphibolites marbles and quartzites are exposed along these structures they display a homogeneous deformation pattern characterized by a generally steeply dipping foliation and a near horizontal to gently plunging mineral stretching lineation indicating a strike slip tectonic regime of deformation along the southernmost fault zone at least various and consistent kinematic indicators including s c structures asymmetric tails of porphyroclasts prove that the strain and metamorphism have been generated by a phase of dominantly non coaxial deformation with a dextral sense of shear 40ar 39ar dating applied on the high grade metamorphic rocks minerals occurring along these zones provide plateau cooling ages closely around 245 ma establishing that this event took place in the lowermost triassic as an early phase of the indosinian orogeny the existence of indosinian movements in vietnam as they have been defined by previous authors during the early century is now accurately confirmed and this is the first insight in the occurrence of ductile strike slip tectonics of indosinian age along nw se fault zones well expressed in central vietnam is a cretaceous thermal and deformational overprint marked by epimetamorphism which took place between 90 and 120 ma as attested by low temperature degassing ages this cretaceous event is not found further north in the song ma zone where younger ages appear as a result of the influence of cenozoic shear movements along the red river fault which displays 20 30 ma ages on the northern flank of song ca in the bu khang phu hoat core complex comparable oligocene lower miocene ages 20 35 ma yielded by biotite and phlogopite reflect a strong overprinting and attest to a rapid uplift of the basement

u pb dating of high temperature metamorphic episodes in the kon tum massif vietnam abstract in vietnam recent studies demonstrated that the kon tum massif was part of the indosinian mountain system together with the truong son belt one sector of the kon tum massif song ba valley is a granulite facies terrain for which ar ar and u pb ages cluster around 245 250 ma in the area of song bien river also metamorphosed under granulite facies conditions ar ar ages of 410 ma are displayed by biotite in this study u pb dating of monazite and zircon has been used to understand the reason for these two groups of ages taking into account the metamorphic mineral assemblages related to granulite facies metamorphism in the two districts for granulites of song ba valley ages of 245 250 ma are confirmed from monazites in the song bien district ages of 465 470 ma displayed by monazites are interpreted to correspond to the metamorphic climax zircons from one of these samples record the age of anatexis that has affected the granulitic rocks the younger age recorded in the song ba valley is considered to reflect high temperature related to charnockitic intrusions emplaced near the end of the indosinian orogeny overprinting the earlier formed granulites and resetting the u pb and ar ar ages for the first time two ht events are dated in the kon tum massif one occurring during the ordovician and the other during the permo triassic

the tam ky phuoc son shear zone in central vietnam tectonic and metallogenic implications abstract the tam ky phuoc son shear zone tkpssz is one of the most pronounced crustal structures in central vietnam and juxtaposes high grade rocks of the kontum massif against lower grade rocks of the truong son fold belt an internal zone comprises highly strained rocks including ultramafic mafic tectonites bounded by mylonitic zones that straddle tens to hundreds of kilometers an external zone comprises mainly high grade metamorphic complexes southern flank and weakly metamorphosed siliciclastic and carbonate rocks with subordinate greenstone northern flank detailed structural analysis reveals that the shear zone is a multi deformed terrane d1 produced a regional high grade schistosity and mylonitization d2 generated regional northwest southeast trending fold arrays and brittle ductile shear zones d3 locally produced northeast trending folds brittle faulting occurred during d4 d5 u pb dating of zircon and monazite suggests that d1 involved metamorphism and felsic magmatism at ca 430 ma recording part of a regional collisional orogeny monazite and titanite growth at ca 250 240 ma in basement rocks is synchronous with widespread syn to post d2 magmatism between ca 260 and 245 ma suggesting a second major collisional event during the indosinian orogeny d3 may have occurred as part of or soon after this permo triassic event deformation during post collisional stages perhaps in response to extrusion wedging and oroclinal rotation of terranes led to post d3 structures d4 d5 the e w trending tkpssz is here shown to be a continuation of the n s trending po ko shear zone pksz most of the significant lode gold occurrences in central vietnam occur along this tkpssz pksz structure and are associated with and controlled by d1 ductile to ductile brittle high strain zones mineralized later stage structures support remobilization and reconcentration of ore during subsequent events at ca 240 ma re os molybdenite age the tkpssz pksz d1 structure likely represents part of a paleosuture zone marking the closure of an ancient ocean basin through terrane assembly in the early paleozoic

mining triggered seismicity governed by a fold hinge zone the upper silesian coal basin poland abstract mining tremor mechanisms and principal stress directions were analysed in order to compare characteristics of seismic events and stress regimes with tectonic settings in the bytom syncline located in the upper silesian coal basin the results of seismic moment tensor inversion calculated for 41 events with magnitudes m2 0 were used to trace changes in types of mechanism normal strike slip reverse with the progress of mining from panel 3 coal seam 503 bobrek mine the data was sourced from the is epos platform an open data infrastructure for the study of anthropogenic hazards linked to georesource exploitation the foci were located below the seam and followed a longwall excavation the computed mechanisms and distribution of spatial temporal events enabled three clusters representing three different stages of stress regimes to be distinguished the calculated principal stress axes indicated the main stress directions present in the studied area enabling a local model of the derivative pattern of neotectonic deformation to be described the regime changed from horizontal extension in the syncline limb first cluster to transpression second cluster to dominating compression in the hinge third cluster resulting in reverse fault production finally the results revealed the causes of seismicity in the studied area and showed that the studied events had been mostly triggered

closure of the east paleotethyan ocean and amalgamation of the eastern cimmerian and southeast asia continental fragments abstract the phanerozoic record of southeast asia preserves the history of opening and subsequent consumption of the paleotethyan ocean and the assembly of continental fragments into asia as part of the broader scale reconstruction of pangea however uncertainty remains as to which of the many suture zones in southeast asia represents the relict of the main ocean when final ocean closure occurred and the assembly history of the eastern cimmerian and southeast asia continental fragments our overview of the geological features of the suture zones the bounding continental fragments and their magmatic metamorphic and sedimentary records resolves many of these key issues the sedimentary biogeographical structural lithological geochemical and geochronological data from the changning menglian inthanon and bentong raub suture zones argue for their linkage with the longmu co shuanghu suture zone in central tibet and together constitute the main east paleotethyan ocean relict the eastward subduction of the ocean resulted in the development of a series of magmatic arc back arc basin and continental fragments in southeast asia including from west to east the lincang sukhothai east malaya arc the jinghong nan sa kaeo back arc basin the simao west indochina fragment the luang prabang loei back arc basin the south indochina fragment the wusu and truong son back arc basins the north indochina fragment the jinshajiang ailaoshan song ma branch back arc basin and the south china block assembly of these fragments resulted in indosinian high temperature and high pressure metamorphism and related tectonothermal event available data indicate a switch from subduction of the main east paleotethyan ocean to the collision of the sibumasu with simao indochina blocks at 237 ma with subsequent syn and post collisional events at 237 230 ma and 230 200 ma respectively along the changning menglian inthanon and bentong raub suture zones the timing of initial syn and post collision events along the jinshajiang ailaoshan song ma suture zone with its record of back arc basin closure is at 247 ma 247 237 ma and 237 200 ma generally 10 ma older than that along the changning menglian inthanon and bentong raub suture zones our synthesis of all available data enables establishment of a comprehensive geodynamic model for the east paleotethyan evolution this model links the spatial temporal pattern across southeast asia into a series of tectonic events including ocean back arc basin opening subduction closure subsequent assemblage and orogenic collapse along with associated igneous metamorphic and sedimentary activities

the early triassic indosinian orogeny in vietnam truong son belt and kontum massif implications for the geodynamic evolution of indochina new structural field data at various scale and 40ar 39ar geochronological results from the basement rocks in the truong son belt and kontum massif of vietnam confirm that ductile deformation and high temperature metamorphism were caused by the early triassic event of the indosinian orogeny in the range of 250 240 ma a compilation of isotopic data obtained in other countries along the sibumasu indochina boundary broadly indicates same interval of ages this tectonothermal event is interpreted as the result of a synchronous oblique collision of indochina with both sibumasu and south china inducing dextral and sinistral shearing along e w to nw se and n s fault zones respectively the collision along song ma follows the northwards subduction of indochina beneath south china and the subsequent development of the song da zone which in turn was affected by the late triassic indosinian phase of shortening within the indochina plate internal collisions occurred coevally in the early triassic as along the poko suture at the western border of the kontum massif

u pb zircon geochronology and geochemistry from ne vietnam a tectonically disputed territory between the indochina and south china blocks volcanoplutonic complexes in ne vietnam have recently been interpreted as intraplate products of the emeishan plume alternatively mafic ultramafic rocks have been considered as dismembered palaeotethyan ophiolites juxtaposed along a tectonic melange zone new u pb zircon geochronological and geochemical datasets presented here suggest a complex geological history that records collision between the indochina south china blocks mafic ultramafic rocks exposed within a tectonic melange song hien tectonic zone include sub alkaline pillow basalts that define two geochemically distinct ophiolitic suites sh 1 n morb like sh 2 transitional e morb like both suites have geochemical signatures suggestive of crustal contamination compatible with a volcanic passive margin rift setting we suggest that sh 1 basalts may correlate with the devonian carboniferous jinshajiang ailaoshan song ma branch of the palaeotethys and form part of the associated dian qiong belt whereas sh 2 basalts are co magmatic with middle late permian mafic ultramafic intrusive rocks dolerites gabbros peridotites that developed in a rift basin most likely on the margin of the down going south china plate during west vergent subduction beneath indochina during continental orogenesis and thrust stacking these ophiolitic rocks were juxtaposed with other lithotectonic blocks within the song hien tectonic zone post collisional relaxation led to the development of a rift basin song hien rift comprising late permian triassic volcano sedimentary strata including 270 265 ma terrigenous sandstones 252 ma mudstones and c 254 248 ma felsic effusives granites and granodiorites were emplaced across ne vietnam between c 252 and 245 ma in a syn to post collisional setting the late permian early triassic felsic magmatic rocks best correlate with coeval rocks in sw guangxi and the central and western ailaoshan fold belts china and the truong son fold belt vietnam together they signal the final to post collisional stages of indochina south china collision we demonstrate that the analysed magmatic rocks in the lo gam song hien domains of ne vietnam are not genetically linked to the emeishan large igneous province in the yangtze block of south china as has been previously widely proposed

partitioning of deformation within several external thrust zones of the appalachian orogen mesoscopic contractional and extensional faults dominate many external thrust zones the fault arrays occur in the hanging walls of some thrusts and in the footwalls of others in a thrust zone from the little mountains fold thrust belt of new york state mesoscopic faults cut and offset a major thrust contact and involved rocks from the thrust s hanging wall and its footwall simultaneously the little mountains exposure indicates that minor faults were active during thrust slip and are not early formed features which were passively translated with the remainder of a sheet when both contractional and extensional mesoscopic faults occur in thrust zones foreland dipping extensional faults overprint contractional faults contractional and extensional microfaults with r 1 and r 2 riedel shear geometries are common in external thrust zone cataclasites and resemble the mesoscopic fault patterns though the evolution of cataclasite layers differs from that of mesoscopic fault arrays contraction and ext

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

sources of the nanwenhe song chay granitic complex sw china ne vietnam and its tectonic significance abstract the nanwenhe song chay complex nscc is a large early paleozoic pluton straddling the border between sw china and ne vietnam it is located at the tectonic junction of the yangtze cathaysia and indochina blocks so that the source of the complex is still enigmatic the rocks from the complex are high k calc alkaline and peraluminous s type granite la icp ms u pb dating of zircons from twelve granitic samples in the complex gives crystallization ages in the range of 436 423 ma zircon u pb hf isotopes and geochemical data show that the nanwenhe granites in the northern part of the nscc probably were mainly derived from neoproterozoic metamorphic pelites analogous to those in the xiajiang and danzhou groups in contrast the song chay granites in the southern part of the nscc were probably derived from neoproterozoic metamorphic psammites analogous to those in the fanjingshan and sibao groups in the southwestern yangtze block the granites from the complex contain abundant inherited zircons with a main peak at 836 808 ma and subordinate peaks at 734 ma and 528 665 ma the inherited zircons have age distribution patterns and hf isotopic compositions similar to those for the detrital zircons from neoproterozoic to early paleozoic sedimentary rocks in the southwestern part of the yangtze block but different from those of the cathaysia block and indochina block therefore the basement of the nscc is equivalent to the yangtze block and the complex may represent the westernmost tip of the early paleozoic orogenic belt in the scb we thus assume that the boundaries between the yangtze block and the cathaysia block and between the scb and icb should be located to the southeast and southwest of the nanwenhe song chay area respectively

first shrimp u pb zircon dating of granulites from the kontum massif vietnam and tectonothermal implications abstract the kontum massif in central vietnam represents the largest continuous exposure of crystalline basement of the indochina craton the central kontum massif is chiefly made of orthopyroxene granulites enderbite charnockite and associated rocks of the kannack complex mineral assemblages and geothermobarometric studies have shown that the kannack complex has severely metamorphosed under granulite facies corresponding to p t conditions of 800 850 c and 8 1 kbars twenty three shrimp ii u pb analyses of eighteen zircon grains separated from a granulite sample of the kannack complex yield ca 254 ma and one analysis gives ca 1400 ma concordant age for a zoned zircon core this result shows that granulites of the kannack complex in the kontum massif have formed from a high grade granulite facies tectonothermal event of indosinian age triassic the cooling history and subsequent exhumation of the kannack complex during indosinian times ranged from 850 c at ca 254 ma to 300 c at 242 ma with an average cooling rate of 45 c ma

paleotethyan evolution of the indochina block as deduced from granites in northern laos abstract the paleotethyan evolution of the southeast asia has become better understood in recent years questions remain however over the role of the dien bien phu suture zone in the evolution of the indochina block and whether the song ma suture represents the boundary between the indochina block and the south china block granitoid geochronological and geochemical data obtained in northern laos provide new information vis a vis these arguments zircon u pb ages together with whole rock trace and rare earth element data from 27 granitic rocks from five complexes allow us to conclude that these granites are typical of i type indosinian volcanic arc granites however the 234 256 ma i type granites mismatch the initiation age obtained from the ductile shear zone of the dien bien phu fault thus repudiating the existence of the dien bien phu suture zone this then implies that the qamdo simao and indochina blocks were united the geochemical and geochronological data further suggest that the main crust in the indochina block formed in the late paleoproterozoic to early mesoproterozoic much later than the archean crustal formation age identified east of the song ma suture moreover the 440 404 ma and 234 256 ma i type granites suggest that the boundary between indochina and south china should be the jinsha river suture song ma suture kontum massif instead of the jinsha river suture song chay suture finally the emeishan basalt and granite complexes both form part of the south china tectonic units subducting westward under the qamdo simao and indochina blocks

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

geologic and metamorphic evolution of the basement complexes in the kontum massif central vietnam abstract this paper presents a regional scale observation of metamorphic geology and mineral assemblage variations of kontum massif central vietnam supplemented by pressure temperature estimates and reconnaissance geochronological results the mineral assemblage variations and thermobarometric results classify the massif into a low to medium temperature and relatively high pressure northern part characterised by kyanite bearing rocks 570 700 c at 0 79 0 86 gpa and a more complex southern part the southern part can be subdivided into western and eastern regions the western region shows very high temperature 900 c and pressure conditions characterised by the presence of garnet and orthopyroxene in both mafic and pelitic granulites 900 980 c at 1 0 1 5 gpa the eastern region contains widespread medium to high temperature and low pressure rocks with metamorphic grade increasing from north to south epidote or muscovite bearing gneisses in the north

a possible solar pacemaker for holocene fluctuations of a salt marsh in southern italy abstract this study is aimed at verifying the possible influence of solar activity on the coastal vegetation development in the tavoliere plain south adriatic region italy between 6350 and 4000 cal bp when regular fluctuations of halophilic vegetation are recorded by pollen a wavelet analysis applied to the percentage values of glasswort vegetation is consistent with periodicities of solar activity and other palaeoenvironmental and palaeoclimate proxies in the literature a comparison of salt marsh pollen indicators salicornia type and ruppia maritima with the 10be dataset from the greenland ice core gisp2 on the basis of their independent chronologies reveals a strong visual correlation indicating that the minima of salt marsh percentages match minima in the 10be curve corresponding to solar activity maxima associated with warm and arid phases at the middle latitudes the tavoliere salt marsh appears to have contracted during the arid warm phases associated to maxima of solar activity and to have expanded during the wet cold phases of solar minima this coastal area characterized by a very flat topography and arid climate appears to have been very sensitive to even minor hydrological and climate changes changes of solar activity determining extensive environmental transformations were also possibly responsible for the abandonment of the human coastal settlements of one of the most important neolithic archaeological districts of italy

crustal anatexis and formation of two types of granitic magmas in the kontum massif central vietnam implications for magma processes in collision zones abstract asia grew in the late permian by the collision of a number of micro continents syn to post collisional magmatism occurred along the continental collision zones in this study we report two types of granitic rocks garnet granite grt granite and orthopyroxene granite opx granite from the kontum massif central vietnam which is situated on the continental collision zone between the south china and indochina cratons these granitic rocks were formed at ca 250 ma when high temperature ht and ultrahigh temperature uht metamorphism took place in the same zone based on the petrological and geochemical features compared with previously reported experimental results garnet bearing granite is derived from pelitic gneisses by partial melting whereas orthopyroxene bearing granite is produced by the partial melting of garnet bearing mafic granulites we inferred that a significantly high geothermal gradient is required to produce vietnamese granitic magmatism and related ht to uht metamorphism this geotherm may be attributed to upwelling mantle plume beneath the kontum massif during the late permian

geochemical and sr nd isotopic constraints from the kontum massif central vietnam on the crustal evolution of the indochina block abstract the kontum massif central vietnam consists mainly of high grade amphibolite to granulite facies metamorphic rocks and represents the largest basement exposure core complex of the indochina block to explore the crustal evolution of indochina sr and nd isotopic and geochemical data for various rock types from the massif are reported the basement rocks show a wide range of present day end values from 22 gneiss to 15 amphibolite yielding depleted mantle model ages tdm from 1 2 to 2 4 ga along with an exceptionally old tdm of 2 7 ga for a granulite these data indicate that crustal formation in the indochina block took place principally during the paleoproterozoic and mesoproterozoic and do not support the conventional notion that the kontum core complex is composed of archean rocks geochemical data indicate that the gneisses and schists have heterogeneous compositions characterized by a calc alkaline nature whereas most of the amphibolites are tholeiitic basalts with intraplate magmatic signatures therefore the former may be interpreted as products from pre existing proterozoic crustal materials and the latter as resulting from the paleozoic rifting event that disintegrated the indochina block from gondwanaland during its accretion with other se asian continental blocks in permo triassic time the indochina core complex was subjected to the indosinian orogeny characterized by a high temperature granulite facies metamorphism in the lower crust with associated charnockite magmatism and subsequent regional exhumation

a systematic test of the hypothesis that the b value varies with depth in california we spatially map the shallow to deep b value ratio in the crust in california previous studies of the frequency magnitude distribution as a function of depth for selected crustal regions indicated that b decreases from b 1 1 in the 0 5 km depth range to b 0 8 in the depth range 7 15 km our detailed mapping confirms that this pattern can be established at the 99 significance level for about 32 of the entire seismically active crust about 2 of the crust displays the opposite b gradient one such area is the san francisco bay area we speculate that differences in stress levels are the main factor controlling the depth dependency of b these results confirm that the b value should not always be considered a constant in studies such as seismic hazard estimations

geodynamic significance of the kontum massif in central vietnam composite 40ar 39ar and u pb ages from paleozoic to triassic abstract the kontum massif of south central vietnam has long been classified as lower continental crust of precambrian archean age u pb zircon and 40ar 39ar biotite ages from charnockites and amphibolite facies rocks from this basement however yield much younger ages and imply at least two paleozoic thermal events syntectonic charnockites from the kannack complex and the southern kontum massif record permo triassic magmatism u pb documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 249 pm 2 end document 2 ma and docume

most likely locations of large earthquakes in the kanto and tokai areas japan based on the local recurrence times abstract we examined the hypothesis that minima in local recurrence time tl or equivalently maxima in local probability pl may map asperities in the kanto and tokai areas of japan where the earthquake catalog of the national research institute for earth science and disaster prevention nied is complete at the m 1 5 m1 5 level we mapped tl pl based on the a and b values of the nearest earthquakes within 20 km of every node of a grid spaced 0 01 for m7 target events only earthquakes within the top 33 km were used the b values increase strongly with depth in several areas therefore some of the tl pl anomalies are not revealed if data from the entire crustal seismogenic zone are mixed thus we mapped tl pl separately for the top 15 km and the rest of the depth range as well as for the entire seismogenic crust the resulting tl and pl maps show that approximately 12 of the total area shows anomalously short recurrence times out of six shallow target events with m 6 5 and which occurred since 1890 five are located within the anomalous areas with tl

detrital zircon ages and heavy mineral composition along the gulf of tonkin implication for sand provenance in the yinggehai song hong and qiongdongnan basins abstract neogene reservoir sand in the yinggehai song hong ygh shb and qiongdongnan basins qdnb was derived from the red river hainan island and the vietnamese truong son belt we investigate the sand dispersal pathways through comparisons of detrital zircon geochronology and heavy mineral analyses of modern vietnamese river sand holocene to recent near coastal sand from hainan island and vietnam and offshore neogene sand and we evaluate the methodologies eleven distinct zircon age clusters characterize the gulf of tonkin provenances red river sand contains the most complex age pattern with 35ma 88ma 155ma 250ma 440ma peaks and broader pre cambrian clusters the 88ma peak uniquely occurs in red river sand northern truong son belt sand contains 35ma 250ma 440ma peaks and pre cambrian clusters comparable to the red river the lack of cretaceous zircons and a high proportion of 250ma relative to 440ma zircons distinguishes the northern truong son belt from the red river the southern truong son belt is characterized by low proportions of 250ma relative to 440ma zircons and the absence of cretaceous and cenozoic zircons hainan island sand is identified by the presence of 100 ma zircons and the absence of cenozoic and 88 ma zircons the zircon age patterns suggest simple although dynamic sand dispersal pathways with mixed sand sources over much of the basins likely resulting from sediment reworking and down stream river merging induced by neogene sea level fluctuations sand in the western ygh shb was mainly sourced from the truong son belt the red river sourced the northern and central ygh shb and qdnb and hainan sand was primarily deposited along the island margin heavy mineral compositions in the gulf of tonkin primarily reflect sediment compositional maturity epidote amphibole pyroxene and garnet indicate immaturity whereas a high zircon content tends to indicate high maturity the use of heavy minerals as provenance indicator should proceed with the utmost caution

the central ailaoshan ophiolite and modern analogs abstract the central ailaoshan cal ophiolite represents an important tectonic component of the jinshajiang ailaoshan song ma suture zone separating the south china and indochina blocks in the mainland se asia the cal ophiolite occurs as a complex tectonic melange and preserves the history of the opening and closure of the once vast jinshajiang ailaoshan song ma branch of the paleotethys new and existing geological data indicate that the cal ophiolite contains magmatic rocks generated by 1 l devonian e carboniferous ca 380 330 ma volcanic passive margin breakup development in the nw gondwana margin 2 l permian ca 258 ma emeishan large igneous province related continental rift magmatism together with and intruded by 3 earliest m triassic ca 244 ma continent continent syn collisional s type granitoids the devono carboniferous suites of the cal ophiolite are highly comparable with many continental margin type alpine tethyan ophiolites in addition the various cal magmatic suites have strong south china block affinities with coeval magmatism particularly in the western south china block jinshajiang song ma and song da terranes