preliminary phanerozoic polar wander paths for the north and south china blocks polar wander paths for the north and south china blocks suggest that 1 both were parts of gondwana in the palaeozoic 2 the north china block accreted to siberia in the late permian and 3 the south china block accreted to the north china block in the middle triassic to the early jurassic comparison of the polar wander path for the south china block with that for northern eurasia suggests that relative motion of over 4 000 km has occurred between them

new paleomagnetic results from northern china collision and suturing with siberia and kazakhstan abstract we report new results from our paleomagnetic studies of the inner mongolia autonomous region in northeastern china and the xinjiang autonomous region in northwestern china primary magnetizations are isolated in tertiary cretaceous late jurassic and late permian rocks and secondary components of magnetization of late jurassic and recent ages are seen in strata of inner mongolia western junggar basin and part of the tarim block suffered widespread complete tectono thermal remagnetization at about 280 ma permian the paleomagnetic evidence suggests that the sampled areas in inner mongolia have been part of the north china block at least since late permian time and the junggar block collided with the tarim block by late permian time our own paleomagnetic results together with available data from other parts of eastern eurasia suggest a tectonic model in which kazakhstan europe and siberia collided with each other and formed the europe siberia kazakhstan plate eur sib kaz in late permian time to the east mongolia outer mongolia inner mongolia and the north china block were also wedged together forming the mongolia north china plate mon nc by this time these two composite continental plates were not a stable unit in the late permian the geometrical relationship of the paleomagnetic poles for these two plates suggests that collision initially occurred in the late permian near the western end 50 n 75 e of the southern siberian fold belt and progressed eastward as the mon nc plate rotated and clockwise about 117 relative to the eur sib kaz plate during the early mesozoic suturing and rotation were probably complete by the late jurassic significant relative motion between the tarim and siberia blocks continued from early triassic to late jurassic as tarim moved northeastward 1400 km relative to siberia

an apparent polar wander path from the tarim block china abstract the apparent polar wander apw path from the tarim block consists of devonian 16 n 165 e a95 4 late carboniferous 41 n 160 e a95 4 permian 61 n 177 e a95 9 early triassic 69 n 183 e a95 11 and jurassic cretaceous 65 n 214 e a95 6 poles on the basis of this apw path we conclude that tarim rode on a plate subducting under the kazakhstan plate between devonian and permian times by the end of the permian subduction had almost finished early triassic poles from tarim siberia north china and south china are discordant indicating post early triassic relative motions among them cretaceous paleomagnetic poles from tarim north china and south china however are consistent suggesting that china has been a coherent tectonic unit since cretaceous time the shape of the apw path from tarim is similar to that of siberia except that tarim s apw path is systematically displaced to the east a 26 clockwise rotation of tarim s apw path about the euler pole 60 n and 14 e reconciles these two apw paths tarim has moved northeastward some 2000 km relative to a fixed siberia since the cretaceous this northeastward motion of tarim with respect to siberia agrees well with the overall cenozoic tectonic style of asia most of southern china has been pushed eastward to give way to the penetrating indian continent east west and northeast trending left lateral strike slip faults north of the tarim block have been documented however the exact amounts of displacement along these faults are not well known using paleomagnetic data from tarim we will also discuss the tectonic evolution of terranes in central asia and the amount of continental shortening in the tibetan plateau

late paleozoic paleomagnetism of south mongolia exploring relationships between siberia mongolia and north china abstract the tectonic evolution of a large region that includes south siberia mongolia and north china is still a matter of fierce debate this is due at least in part to the contentious proposals detailing the kinematics of the major tectonic units in that area one solution to the problem is the acquisition of better defined paleomagnetic data for the various players in the system we carried out a paleomagnetic study of early carboniferous subduction related volcanic rocks of the trans altai zone in south mongolia and successfully isolated a pre folding and presumably primary component from 22 sites a critical analysis of late paleozoic paleomagnetic data from mongolia revealed several problematic data sets while the paleolatitudes derived from more reliable studies agreed well with the expected values for siberia and were consistently different from those for the north china block we also found that late paleozoic declinations from mongolia are rotated counterclockwise through various angles with respect to siberia in addition those rotations are widespread in both inner mongolia and the north china block in this paper we put forward some testable hypotheses and propose a preliminary paleogeographic scheme of the region 1 consistent difference in late paleozoic paleolatitudes between siberia and mongolia on the one hand and the north china block on the other is largely due to strong inclination shallowing in paleomagnetic data for the latter area where most data are from sedimentary rocks 2 widespread counterclockwise rotations in mongolia inner mongolia and north china may be accounted for by a wide zone of sinistral transpression that was active in the early mesozoic 3 in the early mesozoic the mongol okhotsk ocean was much narrower than is usually assumed 4 there was no large scale oroclinal bending between siberia and north china in the permian early mesozoic

palaeomagnetic and structural constraints on 90 anticlockwise rotation in sw mongolia during the permo triassic implications for altaid oroclinal bending preliminary palaeomagnetic results abstract new and published paleomagnetic measurements from trans altai and south gobi zones in south mongolia document large tectonic motions in between late carboniferous and triassic magnetic inclinations confirm equatorial position of south mongolian terranes in late carboniferous permian times the evolution of magnetic declinations indicates 90 anticlockwise rotation in between latest carboniferous and early triassic of all studied tectonic units around the eulerian pole located close to axis of mongolian orocline the anticlockwise rotation continues in triassic being accompanied by a major drift to the north the structural and published geochronological data suggest carboniferous e w shortening of the whole region resulting in n s trend of all continental and oceanic geological units followed by orthogonal n s shortening during late permian to early jurassic both paleomagnetic and geological data converge in a tectonic model of oroclinal bending of mongolian ribbon continent westerly back arc oceanic domain and mongol okhotsk subduction zone to the east the oroclinal bending model is consistent with the coincidence of the eulerian pole of rotation with the structural axis of mongolian orocline in addition the mesozoic collisional tectonics is reflected by late remagnetizations due to formation of wide deformation fronts and hydrothermal activity

palaeomagnetic constraints on the collision and rotation of north and south china the eastern half of china is dominated by the north china block ncb and south china block scb separated by a complex fold system that trends roughly east west interpretation of the geology of this fold belt has led to a variety of estimates of the age of amalgamation of these two blocks1 7 palaeomagnetic results are few and have also been subject to conflicting interpretations8 11 here we present our own palaeomagnetic results for late permian rocks for both the scb and ncb and summarize other relevant palaeomagnetic data by reinterpreting the polarity given in some previous studies we are able to synthesize the results for the widespread emeishan basalts of the scb and to suggest a new model for the collision and relative rotation of the two blocks

genetic links between ash flow calderas and associated ore deposits as revealed by large scale thermo mechanical modeling abstract in addition to a number of epithermal ore deposits some porphyry type ore deposits are also hosted by ash flow calderas spatial correlation between ash flow calderas and these deposits is observed in several parts of the world but temporal correlation between the mineralization and the episode of caldera formation remains unclear especially because geochronological data indicate that the mineralization may date to several million years before or after caldera formation because caldera collapse represents only a very short event in a long time scale evolution between a silicic magma chamber and its host rocks we have developed a thermo mechanical model of upper crustal and magmatic system behavior during the pre and post caldera formation stages major petrophysical properties of ash flow caldera related rocks are incorporated into the model which accounts for brittle elasto ductile rheology and heat transfer and reproduces fault initiation and various caldera collapse scenarios large scale mechanisms of initiation of thermal and structural traps for epithermal ore deposits are described in particular we found that the outer sides of caldera border faults are associated with both anomalous heat transfer and a high fracture density the finite size of the insulating intracaldera units forces the accumulated heat excess to be laterally transferred across the border faults in most cases the model predicts y shaped fault geometry which is surprisingly similar to that of mineralized faults in the field variations in lithostatic pressure on the magma chamber roof and in the vicinity of the border faults can reach 10 to 20 mpa with deep overpressured zones close to the inner edge of the chamber corners despite the fact that hydrothermal convection and fluid geochemistry are not included in the model these thermal and mechanical results are believed to constrain the conditions for mineralization processes our results show that in the presence of regional extension the development of caldera border faults may be suppressed to the advantage of deep seated fractures clustered above the central part of the magma chamber thus favoring conditions for the formation of porphyry type ore deposits finally we demonstrate that well before the eruption the gradual emplacement of a hot and large silicic magma chamber may create significant extensional stress in the brittle upper crust resulting in breakup and pre eruptive normal faulting and thus allowing for conditions of pre caldera mineralization

adularia in epithermal veins queensland morphology structural state and origin four types of adularia i e sub rhombic rhombic tabular and pseudo acicular are recognised from examination of samples from ten epithermal vein deposits and prospects in queensland based on morphology of the individual crystals further investigation of the structural state of adularia reveals that each group has some specific features in terms of the degree of al si disordering which can be related to various crystallisation conditions and the thermal history sub rhombic adularia is commonly 2 4 mm in size and subhedral with more or less rhombic outlines and has a relatively ordered al si distribution 2t1 0 84 reflecting slow crystallisation conditions adularia of this type in association with coarse grained quartz is predominant at deep levels of epithermal systems where boiling is initiated in an environment of low permeability and the fluid is slightly supersaturated with respect to adularia and quartz tabular adularia characterised by its lath shape and disordered structure 2t1 values ranging from 0 64 to 0 74 is likely to have formed when the fluid moves up to a more permeable environment and starts boiling violently relatively high temperatures and rapidly changing conditions account for its special morphology and disordered structure rhombic adularia showing very small crystal size 0 2 mm with euhedral rhombic form has an intermediate degree of al si ordering pseudo acicular adularia is interpreted as pseudomorphs after carbonate and its high al si ordered structure is attributed to the presence of a carbonate precursor these two types of adularia commonly occur within crustiform and colloform bands in association with high grade ore and chalcedony or fine grained quartz which often displays various recrystallisation textures it is most likely that adularias of these two types are formed when extensive boiling is protracted microprobe analyses indicate the composition of all adularia types close to pure kalsi3o8 sericite and or carbonate altered adularias consistently display more ordered structures suggesting that the post crystallisation thermal regime affects the structural state of altered adularia even at temperatures as low as in epithermal environments

magnetism of south mongolian middle paleozoic ophiolites abstract this paper presents new paleomagnetic data from south mongolia middle paleozoic rocks were studied from three different tectonic zones within the south mongolian fold belt from north to south these are the gobi altai zone in terms of paleotectonic position the north shelf of the paleobasin the trans altai zone ophiolite complexes and the south gobia zone the south shelf several paleomagnetic field tests including conglomerate baked contact and fold tests were carried out to determine magnetic stability in addition principal component analysis of the stepwise thermal demagnetization data was used the ophiolites are characterized by three ancient components one magnetic component is pre folding and directed to the south with a very gentle inclination declination d 180 210 inclination i 6 2 k 120 two post folding magnetic components were observed also the first post folding magnetic component has d 282 4 i 36 4 k 30 3 and the second has d 318 6 i 33 0 k 60 5 the final magnetic component is very close to the permian paleomagnetic direction expected from the north china platform the first post folding component of magnetization may have been acquired during the variscan accretion in early carboniferous time when the basin was closed the south mongolian paleo ocean was located in equatorial latitudes near the tarim block the south china platform and probably the north china platform in the devonian

late paleozoic early mesozoic geodynamics of central asia abstract correlation and synthesis of published and new structural paleomagnetic and geochronological data from central asia show the important role of strike slip faulting in their evolution the pattern of major strike slip faults outlines a terrane collage produced by a late devonian early carboniferous collision of the gondwana derived altai mongolia tuva composite microcontinent with siberia and a late carboniferous permian collision of east europe and kazakhstan with siberia the accreted continental margins were cut by strike slip faults and conjugate thrusts into numerous terranes which mixed with one another and disturbed the previous structural and facies framework those complex and multi stage deformations resulted from the late devonian early carboniferous collision of gondwana derived terranes the deformations reached their peak in the late carboniferous permian due to the collision of the kazakhstan east european baltica and siberian continents a system of sinistral strike slip faults formed a mosaic block structure of central asia along the margin of the siberian continent as a result of the late carboniferous permian collision this resulted in the formation of the northern eurasia continent early mesozoic strike slip faulting and conjugate thrusting resulted from the rotation of the siberian and east european cratons

paleomagnetism of the upper proterozoic and devonian rocks from the klodzko metamorphic complex in the west sudetes sw poland tectonic implications for the variscan belt of central europe abstract the klodzko metamorphic complex kmc consists of upper proterozoic metaigneous and metasedimentary rocks forming a stack pile thrusted over the givetian and overlain by frasnian fammenian sediments magnetomineralogical experiments show that the magnetic minerals are secondary the paleomagnetic experiments identified three components of the natural remanent magnetization labeled a1 a2 and m the mean pole positions calculated in situ correspond with the baltica upper devonian a1 plats 18 plonge 317 permo carboniferous a2 plats 39 plonge 2 and triassic jurassic m plats 60 c plonge 308 segments of the apparent polar wander path apwp for baltica this indicates that the region studied was situated close to the baltica plate at least since the upper devonian and was not folded after this period

prospectivity mapping for high sulfidation epithermal porphyry deposits using an integrated compositional and topographic remote sensing dataset abstract the targeting and discovery of epithermal porphyry mineral deposits can be enhanced using a structured quantitative methodology to analyse the distribution of ore deposits and model their spatial association with exploration evidence providing improved understanding on the controls of ore deposition a novel exploration tool integrating field and aster swir and tir satellite imagery has been developed which provides an enhanced means of resolving surface expressions of the residual silica core of the lithocap the alteration zones were clearly resolved by the remote sensing data and an intimate spatial relationship between high grade altered rocks and topographic highs was identified at a number of locations a mineral prospectivity modelling mpm approach parameterized by the results of the remote sensing study using a gis based weighted linear combination implementation of a multi criteria evaluation approach and utilising a fuzzy analytical hierarchy process to elucidate expert knowledge has been implemented to target high sulfidation epithermal porphyry deposits on the island of lesvos greece the results from this integrated altitudinal compositional modelling approach closely matched the hydrothermal alteration mapped in the field supporting the accuracy of this mpm approach

palaeomagnetism and palaeogeography of mongolia in the cretaceous permian and carboniferous preliminary data abstract the paper reports on the results of palaeomagnetic stability tests of oriented samples of lithologically different types of cretaceous permian and carboniferous rocks from northern and southern mongolia the permian andesites and tuffites from three localities barun buren tel tin gol and chulut tsagan del have yielded interesting results groups of normally and reversely polarized andesite tuffs were found even within a single outcrop by means of thermal field demagnetization and multicomponent analysis of the magnetization with a view to the number of samples 177 suitable for analysis and the number of localities 9 the reported palaeomagnetic data should be considered as preliminary the interpreted results indicate a different palaeogeographic evolution of northern and southern mongolia relative to the siberian platform and north china in the permian and carboniferous on the other hand similar apparent polar wander paths for north china lin et al 1985 and the studied regions of northern and southern mongolia indicate similar palaeogeographic evolution in the permian to carboniferous

pongkor west java indonesia a pliocene supergene enriched epithermal au ag mn deposit the pongkor gold silver epithermal deposit with reserves of at least 98 tonnes of gold and 1026 tonnes of silver average grades 16 4 g t au and 171 2 g t ag is one of the most recent and largest gold and silver discoveries in indonesia proven within a short period 1988 1991 40ar 39ar dating on adularia samples give an age of 2 05 0 05 ma the deposit is of the low sulfidation epithermal type and consists of four main mineralized quartz veins located close to the internal rim of a volcano tectonic depression caldera this resulted from an explosive ignimbritic eruption that produced pyroclastic flows and accretionary lapilli with rare intercalations of epiclastic rocks this volcanic unit unconformably overlies miocene subaqueous volcanic andesitic rocks with interbedded epiclastic rocks the mineralized bodies are thick average 4 2 m steeply dipping quartz carbonate adularia veins with a very low sulfide content 0 5 wt their genesis is related to an extensional episode within a tectonic corridor showing nw se and nne ssw conjugate strike slip faults the major vein being located on the inner rim of the caldera the vein fill reveals four successive stages of deposition marked by a specific facies 1 carbonate quartz breccia with dominant quartz and calcite and minor kutnahorite rhodochrosite and rhodonite cq facies 2 a network of banded quartz and former carbonate transformed into manganese oxides through supergene alteration moq facies 3 banded opaline milky quartz boq facies and 4 grey locally banded sulfide rich quartz breccia cutting all the other types gsq facies adularia was deposited at the same time as the quartz the mineralogy and internal structures of the veins crustiform banding vugs collapse breccia clearly indicate a dilational context which is common in low sulfidation epithermal systems gold and silver grades as well as sulfide mineral abundances increase steadily through stages 1 to 4 locally reaching 1 kg t in the gsq facies the sulfides are dominated by pyrite accompanied by common acanthite aguilarite polybasite pearceite and electrum in which the gold content ranges from 48 to 74 wt sphalerite galena chalcopyrite and hessite are fairly rare although present within the cq facies the fluid inclusions of the four facies show homogenization temperatures ranging from 150 to 382 c indicating boiling of a hydrothermal fluid with an initial temperature of around 205 c no marked difference is seen in the gsq facies which has the highest gold content salinities are low generally below 1 wt eq nacl lead isotope compositions of the associated volcanic rocks and the mineralization are very similar 206pb 204pb between 18 706 and 18 814 and between 18 744 and 18 801 respectively demonstrating a genetic link between the pliocene volcanism and the auriferous hydrothermal activity the isotopic signature suggests that the source of the mineralization and associated volcanic rocks is an underlying ancient continental crust that melted and remobilized during the pliocene volcanic and hydrothermal events these conclusions seem applicable to the entire bayah dome the existence of both a tectonic corridor and a caldera favoured channelling of the hydrothermal fluids and the deposition of primary ore in the veins late intense weathering of the ore deposit to depths of 250 m below the surface has given rise to manganese oxide layers limonite zones and silver micronuggets within the veins as well as to gold enrichment

forecasting southern california earthquakes since 1978 and 1979 california has had a significantly higher frequency of moderate to large earthquakes than in the preceding 25 years in the past such periods have also been associated with major destructive earthquakes of magnitude 7 or greater and the annual probability of occurrence of such an event is now 13 percent in california the increase in seismicity is associated with a marked deviation in the pattern of strain accumulation a correlation that is physically plausible although great earthquakes magnitude greater than 7 5 are too infrequent to have clear associations with any pattern of seismicity that is now observed the san andreas fault in southern california has accumulated sufficient potential displacement since the last rupture in 1857 to generate a great earthquake along part or all of its length

late paleozoic polar wander path for the tarim platform and its tectonic significance abstract stepwise thermal and a f demagnetizations have been carried out on 518 samples 47 sites from the sishichang section across the akesu area in the tarim basin the results lead to a discussion on some problems concerning the tectonic history of the tarim platform and adjacent blocks during the late paleozoic from the late carboniferous until the early permian the tarim platform collided with the kazakhstan block siberian platform and russian platform no large displacements have occurred between these blocks since the mesozoic however the permian pole position of the tarim platform obviously differs from that for the sino korea platform the difference in paleolatitude between the tarim and sino korea platforms in the permian was about 10 their orientations were also different the paleomagnetic result is in contrast to the geologically accepted idea that the two platforms in question occur as a whole in the late paleozoic

direction and intensity of the geomagnetic field in the middle devonian and lower ordovician southern mugodjary ophiolites urals abstract a considerable quantity of petromagnetic and palaeomagnetic measurements in the field has allowed us to obtain reliable palaeomagnetic results for such difficult and complex objects as ophiolites eifelian baked sediments diabases dyke contacts and gabbros and tremadocian baked sediments were studied continuous thermocleaning conglomerate and fold tests were applied the palaeointensity was investigated by means of several palaeomagnetic methods wilson burakov van zijl shaw and bagina petrova the mean intensities of the geomagnetic fields are 7 and 16 5 t with mean palaeomagnetic pole positions of 9 n 134 e and 6 s 83 e respectively these data demonstrate that southern urals mugodgary was located near the northern margin of the east european plate during ordovician devonian time the allochthonous crustal oceanic plate was thrust upon the edge of the plate and deformed as late as the permian changes in the polarity of the geomagnetic field are recorded in the succession of sheeted dykes a direct corroboration of the vine mathews hypothesis