miocene to present activity along the red river fault china in the context of continental extrusion upper crustal rotation and lower crustal flow detailed mapping of field relationships along the red river fault reveals information about the distribution and magnitude of slip along the fault about its interactions with other regional fault systems and the relationship between river incision and growth of the eastern margin of the tibetan plateau the red river fault is complex consisting of up to four strands and is dominated by right lateral strike slip displacement evidence for an extensional component of displacement is strongest along the northern part of the fault and decreases to the southeast to zero southeast of a major bend in the fault results of this study indicate dextral displacement on the red river fault is probably at least 40 km 15 16 km of which predates incision of the red river in pliocene time or later and probably also predates plateau growth and development of other regional fault systems long term average slip rate on the red river fault is a minimum of 5 mm yr however regional active tectonics are characterized by rotation of the upper crust around the eastern himalayan syntaxis bounded to the east by the xianshuihe xiaojiang fault system which deflects but does not cut the red river fault the distributed nature of the xianshuihe xiaojiang fault system as it approaches the red river fault is important for accommodating shearing across the strong crustal anisotropy formed by the red river fault and ailao shan shear zone the red river fault appears to terminate in the extending dali fault system in northwest yunnan pliocene surface uplift river incision and rotation around the eastern himalayan syntaxis are inconsistent with the pre pliocene displacement on the red river fault and lateral extrusion along the ailao shan shear zone advocated by the extrusion model this suggests a significant change in crustal conditions on the southeast margin of the tibetan plateau in pliocene time possibly the result of lower crustal flow

kinematics of cenozoic extension on the south china sea continental margin and its implications for the tectonic evolution of the region abstract in the northern south china sea several large sedimentary basins developed during the cenozoic characterized by episodic rifting clockwise rotation of the rifts an eastward aging breakup unconformity and intensifying crustal extension to the east these features may be summarized by a scissors model the maximum rifting occurred north of the maximum thermal subsidence which was in turn north of the seafloor opening in contrast the nansha microcontinent south of the south china sea basin was dominated by compressional deformation during the cenozoic extension was of subordinate significance and manifested mainly by block faulting and tilting in the late early oligocene maximum tilting occurred in the southern part of the nansha microcontinent at distance from the deep sea basin of the south china sea the asymmetric development of extensional structures around the south china sea basin may be explained by the simple shear model proposed by wernicke 1981 the tectonic development of the south china sea was the consequence of various interactions of three major plates and may be summarized into three stages with dominating influences of respectively the retreat of the west pacific subduction zone in the late cretaceous the hard collision and impinging of india to tibet since the late eocene and the fast northward subduction of the indian ocean australian plate since the late early miocene

a quaternary solution model for white micas based on natural coexisting phengite paragonite pairs a thermodynamic model for the quaternary white mica solid solution with end members muscovite mg celadonite paragonite feceladonite ms mgcel pg fecel is presented the interaction energies for the mgcel pg join the fecel pg join and the ternary interactions were obtained from natural coexisting phengite paragonite pairs phengite paragonite pairs were selected based on the criteria that their chemical compositions may be represented as a linear combination of the model end member compositions and that the respective formation conditions 350 650 c 4 21kbar are accurately known previously published excess free energy expressions were used for the ms pg ms mgcel and ms fecel binaries the suggested mixing model was tested by calculating multicomponent equilibrium phase diagrams this proved to be particularly well suited to reproduce compositional variations of white micas from amphibolite facies metapelites

the contact aureole of the south mountain batholith in halifax nova scotia geology mineral assemblages and isograds the contact aureole at the eastern margin of the south mountain batholith halifax pluton underlies most of the city of halifax nova scotia the halifax group in the study area includes two lithological units the cunard and bluestone formations before intrusion both had been affected by greenschist facies regional metamorphism and deformed into northeast southwest trending regional upright folds associated with a strong slaty cleavage contact metamorphic isograds trend obliquely across the halifax peninsula at a high angle to regional structural trends at 2 5 3 km from the intrusive contact sparse cordierite spots mark the outer limit of the contact aureole the biotite in isograd is marked by the development of biotite within chlorite muscovite stacks inherited from regional metamorphism pyrrhotite is the dominant sulphide mineral throughout the contact aureole with increasing metamorphic grade assemblages in both units are marked by increasing modal abundance of cordierite and biotite with k feldspar variably developed within ca 600 m of the contact however there is a marked difference in the distribution and appearance of andalusite between the two units in aluminous pelites of the cunard formation idioblastic chiastolite appears before biotite more than 1500 m from the contact in the less aluminous bluestone formation andalusite is present only within ca 500 m of the contact where it forms xenoblastic spongy crystals in both units the assemblage andalusite biotite k feldspar cordierite is developed near the contact with local fibrolite and evidence of incipient partial melting petrographic constraints suggest pressure temperature conditions at the contact of ca 2 5 3 0 kbar 1 kbar 100 mpa at ca 650 c

the multiple inverse method a new technique to separate stresses from heterogeneous fault slip data abstract a new inverse technique is presented here to separate stresses from heterogeneous fault slip data without a priori information on the stresses or on the classification of faults according to the stresses four parameters are determined by the inversion one for the shape of the stress ellipsoid and three for the direction of the stress axes accordingly the inversion is equivalent to the projection of the fault slip data to a point in four dimensional parameter space the data are divided into k element subsets to which the inverse technique is applied where k 4 or 5 is the optimal choice for the stability of solutions and for the reduction of computation significant solutions are identified as clusters in parameter space the technique is demonstrated first by simulated fault slip data as an example field data obtained from miocene fore arc sediments in western japan were processed by the method

paleomagnetic study of permian and mesozoic sedimentary rocks from northern thailand supports the extrusion model for indochina abstract the mode of deformation of southeast asia resulting from the indian collision is still controversial is convergence between stable india and siberia absorbed principally by crustal shortening and thickening and minor strike slip faulting or by a mechanism of extrusion involving crustal thickening and lateral escape of blocks along major strike slip zones in order to test these models we have carried out a paleomagnetic study of sedimentary rocks of jurassic to cretaceous age on the khorat plateau in thailand a large discrepancy between the poles of indochina presented in this paper and a compilation of south china block pole positions both at the triassic jurassic and the jurassic cretaceous boundary imply some 1500 800 km of post middle cretaceous left lateral slip along the red river and xian shui he fault zones and approximately 14 7 of clockwise rotation for the indochina block relative to the south china block such relative motions are in agreement with a model of lateral extrusion of indochina during the india asia collision additional data of permian upper triassic and lower jurassic age collected in indochina indicate a post late permian remagnetization for the upper permian limestones a comparison of these data with those from yunnan south china the north china block and the south china block shows that these blocks have probably been in contact at least since the late triassic

intermediate sodium potassium mica in hydrothermally altered rocks of the waterloo deposit australia a combined sem emp xrd tem study metastable intermediate na k mica represents a product of hydrothermal alteration in volcanic rocks from the alteration halo of the waterloo massive sulfide deposit australia the xrd pattern of this solid solution between paragonite and muscovite is characterized by a rational series of basal reflections with d values intermediate between the end members transmission electron microscopy revealed that the intermediate na k mica forms thick stacks that belong to a two layer polytype na rich intermediate na k mica typically occurs together with paragonite whereas k rich intermediate na k mica is intergrown with muscovite the intermediate na k mica is interpreted to have formed as a result of the incomplete transformation of k rich mica to na rich mica through dissolution and recrystallization processes driven by compositional changes of the hydrothermal fluids interacting with the volcanic rocks alteration must have proceeded under non equilibrium conditions because the composition of the solid solution falls into the miscibility gap separating paragonite and muscovite

an experimental study of skin friction around piles in clay load tests on a model pile installed in speswhite kaolin are described the soil surrounding the pile was consolidated under a range of stress ratios k and the pile was loaded under drained conditions in such a way that only shaft friction was generated pile installation techniques minimized soil disturbance so that the failure criterion for pile shaft friction could be investigated the results based on tests on nine normally consolidated and one overconsolidated sample show that the angle of shaft friction is independent of the stress ratio in the soil before loading 0 7 k 1 5 and is only justless than triaxial for normally and overconsolidated kaolin when loaded axially the lateral stresses on the pile shaft decrease with increasing shaft load for normally consolidated soil and increase on loading in overconsolidated soil differences between adhesion factors back calculated from the model tests and those normally encountered in practice highlight the effects of disturbance caused by mo

axial capacity of bored piles in very stiff intermediate soils there is a major shortage of good quality load test data for bored piles in stiff to hard intermediate soils such as silts and clayey sands this paper presents the results and interpretation of an

petrology of hp metamorphic veins in coesite bearing eclogite from western tianshan china fluid processes and elemental mobility during exhumation in a cold subduction zone abstract a petrological study was carried out for high pressure hp veins which cut through the host coesite bearing eclogites at habutengsu kebuerte in western tianshan china the results place constraints on the origin and property of metamorphic fluids during subduction zone metamorphism omphacite clinozoisite and quartz dominated veins occur on centimeter to meter scales within lens shaped and layered eclogites or cutting into the country rocks of garnet phengite schists coesite bearing eclogites mainly consist of fibrous fine grained omphacite and porphyroblastic garnet with minor amounts of amphibole mainly barroisite clinozoisite white mica mainly paragonite and rutile the veins are pronouncedly coarse grained compared to the host eclogites and commonly consist of quartz clinozosite rutile white mica phengite and paragonite and garnet with or without omphacite titanite apatite carbonate mainly dolomite and glaucophane fluid inclusions are abundant in vein omphacite titanite and apatite but are rare in the equivalent minerals of host eclogites rounded vein garnets usually occur close to the sharp interface of vein and host eclogite omphacite in the veins is characterized by its euhedral form surrounded by quartz or coarse bladed aggregates in contrast to the fibrous or patchy one suggesting dynamic recrystallization in the host rocks omphacite in both veins and host eclogites has similar jadeite contents jd 40 50 indicating formation at eclogite facies metamorphic conditions vein phengite uniformly contains certain amounts of ba with maximum bao content of 3 16 4 25 wt suggesting that ba was mobilized during the exhumation of uhp rocks specific textures of vein minerals such as the enclosure of magnesite or calcite in dolomite rutile in titanite and the occurrence of zoned ba rich phengite indicate the chemical variability of channelized fluids over time based on zr content in rutile and the presence of paragonite omphacite phengite glaucophane as well as the little deformed textures of hp veins it is estimated that the vein forming fluids would flow at about 1 3 2 1 gpa and 540 580 c corresponding to the stage of retrograde eclogite facies recrystallization during exhumation of the uhp eclogites that formed at peak p t conditions of 2 7 gpa and 460 520 c the hp veins occur as a consequence of a regional tectonothermal event triggering breakdown of lawsonite within the uhp eclogites based on the petrology of vein minerals it is inferred that the hp fluids were enriched in si ca na al and ba this suggests that these elements could be mobilized during the retrograde metamorphism of uhp eclogites in a cold subduction zone coeval pervasive flow of hp metamorphic fluids through the uhp eclogites at this stage may be an important process to eliminate most mineralogical evidence of the uhp metamorphism

neotectonic regime on the passive continental margin of the northern south china sea abstract between 1989 and 1994 more than 6600 km of reflection seismic profiles were obtained in the south china sea off hong kong with the german research vessel sonne during cruises so 50b so 72a and so 95 a seismo stratigraphic interpretation of this data set leads to a new age assignment of the unconformity t0 which we place within the pleistocene both neogene unconformities t1 and t0 are generated by uplift of the dongsha rise and truncation of their overlying strata this uplift is caused by intrusion of magma into the upper crust our seismic profiles show plutons which have penetrated the sedimentary cover whereby their original stratification in the contact zone is eliminated these magmato tectonic events may be correlated to the two main collision phases between taiwan and the continental margin of east china 5 3 and 3 0 ma ago the collisional events subsequent to the nnw to wnw drift of taiwan transformed the compression into strike slip movements along the continental margin of southeastern china the accompanying stress regime is transtensional with subsidence of the cooling oceanic crust since the cessation of rifting and its consumption beneath the manila trench providing the extensional stress the strike slip movements remobilized many of the rift and drift faults providing pathways for magma ascent the tectonic framework of the northern south china sea is characterized by miocene faults trending ne sw these faults are scarce but are distributed throughout the study area pliocene faults striking ene wsw to ne sw are concentrated west of the dongsha islands and are mostly strike slip in character recent faults are generally oriented ne sw subparallel to the synrift faults they result in part from local uplifts where they are normal in character but strike slip motion also occurs most of the faults involve the basement and represent reactivated zones of weakness of the rift and drift phases

polyphase rifting of greater pearl river delta region south china evidence for possible rapid changes in regional stress configuration abstract the greater pearl river delta prd region consisting of several late mesozoic cenozoic basins has preserved information on the tectonic history of the coastal region of south china an integrated morphological and structural study of the basins has revealed several phases of extension subsequent to the collapse of the mesozoic arc magmatism a n s extension associated with the exhumation of the magmatic arc during the late mesozoic early cenozoic was followed by an ene wsw extension producing nw striking normal faults in the region paleo stress analysis of fault slips measured at seven localities reveals stress configurations consistent with the field observation the basin development during the cenozoic was strongly controlled by relative motion of neighboring plates as well as pre existing structures the results suggest that stress configuration can change relatively rapidly in a continental margin undergoing a transition from an active margin to passive margin

experimental reversal of the na k exchange reaction between muscovite paragonite crystalline solutions and a 2 molal aqueous na k cl fluid

mesozoic felsic arc magmatism and continental olivine tholeiites in zhejiang province and their relationship with the tectonic activity in southeastern china abstract the mesozoic geology of zhejiang province in southeastern china is characterized by two distinct geodynamic settings separated by a major tectonic event during the late jurassic early cretaceous a continental magmatic arc developed with a westward subduction of the kula or izanagi plate under the south china block during the development of this magmatic arc microsyenite porphyries and quartz bearing porphyries were emplaced in western zhejiang about 124 ma ago these porphyritic rocks intruded felsic tuffs that rest unconformably on carboniferous and permian folded strata geochemically they are enriched in lil and light rare earth elements lree which are features of acid shoshonitic suites isotopically they are characterized by negative nd t 124 5 3 to 4 7 values and high initial 87 sr 86 sr ratios 0 7079 0 7084 later in eastern zhejiang quartz phyric ignimbrites and subordinate acid andesites were emplaced and intruded by nearly contemporaneous microsyenitic and rhyolitic domes during the cretaceous about 97 ma ago all these rocks belong to the high k calc alkaline suites they show geochemical features of volcanic arc granites emplaced in an active continental margin and are characterized by negative nd t 97 8 8 to 7 1 and high initial sr isotopic ratios 0 7081 0 7089 the negative nd t 97 values of all the cretaceous calc alkaline and shoshonitic rocks of intermediate to acid composition suggest that these rocks were probably derived from a mantle wedge source contaminated by variable amounts of old crustal components likely represented by the proterozoic basement rocks of the south china block the contemporaneous igneous rocks in vietnam as well as in the fujian and guangdong provinces china represent the lateral counterparts of the zhejiang calc alkaline plutonic and volcanic rocks in the late early cretaceous an important tectonic event occurred which provoked the ending of the inagazi or kula plate subduction and affected the continental magmatic arc this tectonic event is likely related to the collision of the china indochina margin with the west philippine block after this tectonic event in the beginning of the late cretaceous continental stretching and crustal attenuation affected the south china block leading to the development of ne sw faulted basins in which continental olivine tholeiites and minor alkaline rhyolites were erupted both characterized by low nd t 97 ratios ca 4 meanwhile continental conglomerates and sandstones were also deposited this rifting process began likely before the india asia indentation and lasted at least until the late tertiary

the hydrostatic corer selcore a tool for sediment sampling and geophysical site characterization hydrostatic energy is used to power an active device for sediment sampling and geophysical site characterization in the selcore design a steel tank with built in drive unit constitutes the core head the difference between ambient water pressure and atmospheric pressure in the tank provides the energy the selcore prototype enters the seabed as a gravity corer and automatically shifts into pile driving mode with up to 52 duty cycles without the need for an external trigger mechanism the corer has operated in water depths from 300 to 3500 m operation at depths shallower than 300 m including on dry land can be facilitated using auxiliary water pressure penetration and recovery is generally more than two times the performance of a gravity corer of equivalent weight the added utilization of hydrostatic energy has particular advantage in cases of relatively high shear strength sediments as well as attempts to core shallow bedrock below a sediment cover selcore has potential as a seabed seismic hammer source and initial land tests show good signal repeatability estimates of sediment thickness and seismic velocity obtained from the inversion and interpretation of the dominant rayleigh surface waves corresponds closely to the shallow borehole stratigraphy at a land test site

use of two new na li geothermometric relationships for geothermal fluids in volcanic environments abstract this work has made it possible to obtain two new na li geothermometric relationships in addition to the three already known fouillac and michard 1981 kharaka et al 1982 and confirms that the na li geothermometer unlike the na k na k ca k mg and silica geothermometers or the isotope 18o h2o so4 geothermometer also depends on the fluid salinity and the nature of the reservoir rocks reacting with the geothermal water one of the relationships concerns the fluids derived from seawater basalt interaction processes existing in emerged rifts such as those of iceland reykjanes svartsengi and seltjarnarnes geothermal fields and djibouti asal ghoubbet and obock geothermal areas or in numerous oceanic ridges and rises mid atlantic and middle valley ridges east pacific rise etc the best adapted na li relationship for geothermal fluids discharged from emerged rifts between 0 and 365 c is t k 920 log n a l i 1 105 r 2 0 994 n 27 where na and li are the aqueous concentrations of these elements given in mol l the other na li relationship was determined using dilute waters collected from wells located in different high temperature 200 325 c volcanic geothermal areas of iceland krafla namafjall nesjavellir and hveragerdi this relationship can be expressed as follows t k 2002 log na li 1 322 r2 0 967 n 17 these two relationships give estimations of temperature with an uncertainty close to 20 c the second na li relationship was also successfully applied to ht dilute geothermal waters from the east african rift ethiopia kenya some case studies in the literature and thermodynamic considerations suggest that the na li ratios for this type of fluids could be controlled by full equilibrium reactions involving a mineral assemblage constituting at least albite k feldspar quartz and clay minerals such as kaolinite illite or muscovite and li micas unlike the na li ratios no thermometric relationship using li isotopes could be determined for this type of water however it was noticed that 7li values higher than 16 are always associated with low to medium temperature waters

crustal structure inferred from gravity anomalies in south china abstract the bouguer gravity anomaly map of the mainland of south china and the south china sea compiled from the most recent 1 500 000 and 1 1 000 000 gravity data is presented the distribution of faults including the secondary faults which can be located by a method based on cross correlation between the theoretical anomaly due to a vertical step and the second vertical derivative of the bouguer anomalies large strike slip faults without vertical displacement or with a small throw which are difficult to identify on the bouguer gravity map and can be inferred from the distribution of the secondary faults and major faults inferred from the zones of gravity gradients on the bouguer gravity map is presented also comparison of the regional gravity anomalies with known density interfaces deduced from seismic data and geological maps shows that the main geological factors causing gravity anomalies are granites low velocity layers in the upper crust the moho discontinuity and the upper crustal thickness variations the broad trend of gravity anomalies depends mainly on the moho and the upper crustal thickness variations we have attempted to isolate approximately the anomalies due to the upper crustal thickness variations by subtracting the anomalies due to the moho from the regional anomalies and then the upper crustal thickness in south china can be estimated by inversion of the gravity anomalies

the effects of ferromagnesian components on the paragonite muscovite solvus a semiquantitative analysis based on chemical data for natural paragonite muscovite pairs chemical data for 139 natural paragonite muscovite pg ms pairs illustrate the effects of ferromagnesian components on the p t x topology of the pg ms solvus the pairs were selected on the basis of reasonably accurate knowledge of the p t conditions of formation evidence for close approach to equilibrium at peak metamorphic conditions exclusion of pairs in which paragonite contains more than 5 mol margarite and exclusion of pairs from polymetamorphic rocks that contain more than one set of cogenetic pg ms pairs graphical analysis reveals considerable scatter in the data nevertheless it is evident that the muscovite limb of the solvus shifts markedly toward end member muscovite with increasing pressure from approximately 7 kbar to 21 kbar this shift is attributed to a pressure induced increase of the ferromagnesian content of muscovite which increases the size of the xii alkali site to the effect that k is more readily accommodated than na the data also suggest that the paragonite limb of the solvus migrates slightly toward end member paragonite with increasing pressure broadening of the pg ms solvus with increasing pressure reflects increasingly nonideal na k mixing as the phengite content of muscovite increases due to the wide scatter of data for pg phengitic ms pairs it is concluded that at the present time pg ms solvus thermometry is only viable for quasibinary pg ms pairs

extensional tectonics within a subduction type orogen the case study of the wugongshan dome jiangxi province southeastern china abstract in southeastern china the wugongshan massif consists of metamorphic rocks and granites generally considered as basement rocks formed during an early paleozoic orogeny our structural and radiometric reappraisal of this massif shows that it results from a mesozoic doming in the metamorphic rocks the foliation defines an e w elliptical shape and bears a n s stretching lineation the axial zone of the dome is occupied by oriented plutons the outer part of the dome consists of devonian quartzite carboniferous permian limestone and triassic jurassic sandstone ductile deformation observed in the permian carbonates and older units develops contrasting kinematics the northern and southern flanks present top to the north and top to the south motions respectively the same divergent pattern of motion is recorded from brittle structures up to the jurassic sandstone the late cretaceous red beds are undeformed in the axial zone coaxial flow indicated by symmetric pressure shadows and quartz fabrics predominates along the n and s flanks of the dome post folial recumbent folds are symmetrically overturned to the n and s respectively but at the two extremities of the dome the fold axes are parallel to the stretching lineation 40 ar 39 ar ages of biotite and muscovite from mylonite and granite suggest a late triassic age for the ductile deformation and an early cretaceous age for the final doming the wugongshan dome is similar to a metamorphic core complex formed in an extensional tectonic regime a model which emphasizes plutonism is discussed from permian to early cretaceous southeastern china was a subduction type orogen the crust of which was thickened by accretion of mantle derived magmas the emplacement of a large amount of mesozoic granitoids in southeastern china promoted thermal softening and gravitational instability that allowed the crust to extend the formation of the wugongshan dome and other metamorphic core complexes appears to be a the direct consequence of plutonic activity and crust rheology

late cretaceous genesis of the kula plate abstract we propose that the pacific kula ridge began spreading approximately 85 m y b p during late cretaceous time extrapolation of the great magnetic bight backwards in time results in an implausible ridge configuration this implies that plate velocity vectors for the pacific kula and farallon plates were not constant during this interval evidence for splitting of the kula plate from the pacific plate along the chinook trough is the relationship between the north striking amlia and adak fracture zones the chinook and emperor troughs and the magnetic lineations south of the aleutian trench if this hypothesis is correct it will require that mesozoic reconstructions of the pacific basin and their relation to cenozoic reconstructions be re examined a previously unrecognized mesozoic plate may be required we propose calling this the izanagi plate

relating shaft friction of buried piles and cpt resistance in clayey sands this paper examines factors controlling the ultimate shaft friction developed on buried piles in normally consolidated clay sand mixtures and explores the relationship between this friction and the

tectonic characteristics and evolution history of the pearl river mouth basin abstract on the basis of the new understandings from tens of thousand of kilometres of geophysical material and over 60 exploration and evaluation wells providing data on the pearl river mouth basin prmb this paper analyses the special tectonic position of the prmb where three major plates i e the eurasian the pacific and the indo australian plates meet and interact the characteristics of the basin geological structure and its tectonic evolution are also discussed situated on continental and transitional crust the prmb is a mesozoic cenozoic oil and gas bearing basin developed on caledonian folding basement which was reformed during the mesozoic in the process of its formation and evolution the prmb underwent extension slight compression and re extension with the eruption of intermediate acid and basic magma meanwhile it formed double structural layers with faulting below and depression above and sediments were laid down with marine facies following continental facies hydrocarbons accumulated from continental source rocks in the marine reservoir rocks by using a fracture structure model of the uplift and depression the mechanism of the prmb and its evolution history have been interpreted

tectonics of south china key to understanding west pacific geology abstract south china is not a post caledonian platform but a composite of orogenic belts this late proterozoic mesozoic orogen is a collage of three continental fragments the three blocks are yangzi huanan and dongnanya and they are separated by the banxi nanpanjiang formerly xianggangzhe and gunanhai suture zones yangzi was separated from gondwanaland during late precambrian when an open ocean called banxi was present between the two continents tectonic processes at an active margin during sinian and early paleozoic time led to the genesis of an accretionary wedge complex the banxi melange and the huanan flysch nappes on the northern margin of huanan which was then the northern margin of the gondwana continent reorganization of plates during the devonian suspended subduction at the huanan active margin huanan was uplifted and unconformably overlain by transgressive deposits of devonian and or carboniferous age a remnant ocean the nanpanjiang sea still existed between yangzi and huanan and deep water sedimentation continued both at the southern margin of yangzi and at the northwestern margin of huanan the latter again became an active margin during late paleozoic when permian and triassic flysch sediments were deposited in foredeeps ahead of advancing nappes huanan and yangzi collided during the triassic and resulted in the deformation of the passive margin of the latter to form the yangzi deformed belt huanan was separated from a more southerly continent dongnanya in the devonian by seafloor spreading which created a late paleozoic and early mesozoic ocean gunanhai ocean a continuously deposited sequence ranging in age from devonian to triassic was laid down on the southern passive margin of huanan on the other side of the ocean the dongnanya permian strata include glacial marine deposits of gondwanaland affinity dongnanya became separated from gondwanaland during the late permian when it marched northward to be reunited with huanan the huanan passive margin sequence was deformed by folding and overthrusting after the late mesozoic collision of huanan and dongnanya scattered outcrops of the suture melange resulting from this collision occur at a few localities in coastal fujian dongnanya in our model was the mesozoic continent of southeast asia peripheral to mainland asia this may or may not have been the eastern continuation of the microcontinent sibumasu siam thailand burma malaysia sumatra the collision of dongnanya and asia gave rise not only to the gunanhai melange of coastal fujian but also to the ophiolite melanges parts of which are present in taiwan tailuko the philippines and western malaysia

oligocene miocene bu khang extensional gneiss dome in vietnam geodynamic implications a large oligocene miocene extensional gneiss dome in vietnam has implications for the kinematics of the ailao shan red river shear zone and rifting of the south china sea a major northeast dipping extensional shear zone separates the bu khang dome from less metamorphosed units above shearing deformation occurred during the exhumation of high pressure rocks 40 ar 39 ar ages on micas reveal oligocene miocene ages from 36 to 21 ma after a high pressure episode of probable oligocene age the area was subjected to northeast southwest extension during the opening of the south china sea a kinematic model involving left lateral shear and block rotation within a north south dextral shear zone integrates our observations in the bu khang dome with south china sea rifting

characterization of non equilibrium and equilibrium occurrences of paragonite muscovite intergrowths in an eclogite from the sesia lanzo zone western alps italy coexisting muscovite and paragonite have been observed in an eclogite from the sesia lanzo zone western alps italy the p t conditions of this eclogite reached 570 650 c and 19 21 kbar and the rocks show several stages of mineral growth during their retrograde path ranging from the subsequent lower p eclogite facies to the blueschist facies and then the greenschist facies muscovite and paragonite are very common in these rocks and show two texturally different occurrences indicating equilibrium and non equilibrium states between them in one mode of occurrence they coexist in equilibrium in the lower p eclogite facies in the same rock muscovite albite also replaced paragonite during a greenschist facies overprint as evidenced by unique across 001 layer boundaries the chemical compositions of the lower p eclogite facies micas plot astride the muscovite paragonite solvus whereas the compositions of the greenschist facies micas lie outside the solvus and indicate disequilibrium the tem observations of the textural relations of the greenschist facies micas imply structural coherency between paragonite and muscovite along the layers but there is a sharp discontinuity in the composition of the octahedral and tetrahedral sheets across the phase boundary we propose that muscovite formed through a dissolution and recrystallization process since no gradual variations toward the muscovite paragonite interfaces occur and no intermediate homogeneous na k phase has been observed because a solid state diffusion mechanism is highly unlikely at these low temperatures 300 500 c especially with respect to octahedral and tetrahedral sites it is assumed that h2o plays an important role in this process the across layer boundaries are inferred to be characteristic of such non equilibrium replacement processes the characterization of these intergrowths is crucial to avoiding erroneous assumptions regarding composition and therefore about the state of equilibrium between both micas which in turn may lead to misinterpretations of thermometric results

thermodynamic mixing models for muscovite paragonite solutions based on solution calorimetric and phase equilibrium data enthalpies of solution have been measured on a series of muscovite paragonite micas in 20 1 hf at 50 c under isoperibolic conditions the molar enthalpy of formation of paragonite at 298 k for which no calorimetrically measured value is currently available has been determined to be 5937 5 3 kj an inversion of all calorimetric volumetric and phase equilibrium data has been performed giving a range of mixing models compatible with most experimental data the following expressions of the mixing properties of 2m 1 micas for enthalpy h ex and volume v ex at pressures up to 10 kbar forcing excess entropy s ex to be zero and using a subregular mixing model are favoured h ex kj 10 6 4 45 1 2x ms x ms 1 x ms v ex j bar 0 452x ms 1 x ms however mixing models of higher order with asymmetric negative s ex are also possible

continentward dipping detachment fault system and asymmetric rift structure of the baiyun sag northern south china sea abstract the rift architecture and deep crustal structure of the distal margin at the mid northern margin of the south china sea have been previously investigated by using deep seismic reflection profiles however one fundamental recurring problem in the debate is the extensional fault system and rift structure of the hyperextended rift basins baiyun sag and liwan sag within the distal margin because of the limited amount of seismic data based on new 3d seismic survey data and 2d seismic reflection profiles we observe an array of fault blocks in the baiyun sag which were tilted towards the ocean by extensional faulting the extensional faults consistently dip towards the continent beneath the tilted fault blocks and extensional faults a low angle high amplitude and continuous reflection has been interpreted as the master detachment surface that controls the extension process during rifting the continentward dipping normal faults evolved in a sequence from south to north generating the asymmetric rift structure of the baiyun sag the baiyun sag is separated from the oceanic domain by a series of structural highs that were uplifted by magmatic activity in response to the continental breakup at 33 ma and a ridge jump to the south at 26 24 ma therefore we propose that magmatism played a significant role in the continental extension and final breakup in the south china sea

oligo miocene midcrustal subhorizontal shear zone in indochina new structural observations of oligo miocene deformation in north vietnam along the red river shear zone suggest that left lateral strike slip shear was restricted to the upper and middle crust above a horizontal shear zone left lateral shear deformation is associated with low pressure low temperature parageneses high temperature deformation is restricted to zones where the foliation has a low dip in the core of the dai nui con voi antiformal dome these observations complete those made earlier in the bu khang extensional dome farther south above the horizontal shear zone left lateral transpression was active during the first stage and changed to transtension some 33 myr ago purely extensional metamorphic domes bu khang or transtensional domes dai nui con voi were exhumed during this younger stage our observations plead for caution when interpreting strike slip structures at lithospheric scale