a deforming plate tectonic model of the south china block since the jurassic abstract the south china block has experienced multiple phases of tectonic deformation since the middle jurassic understanding this deformation history helps reveal the driving mechanisms responsible and sheds light on the associated magmatism and mineralization here we construct deformable plate tectonic reconstructions for the south china block from 170 ma to the present using gplates the deformation starts with a nw se oriented shortening phase from 170 to 136 ma subsequently south china experienced two episodes of extension in the cretaceous during 136 118 ma and 100 80 ma respectively the cenozoic extension occurred mostly along the southeast continental margin including the east china sea shelf basin and rift basins in the northern south china sea margin and the taiwan margin segment the rifting was initiated nearly simultaneously along the continental margin at 65 ma and ceased at 34 30 ma the northern portion of the okinawa trough started rifting at 15 ma while the southern portion rifted in the last few million years the luzon volcanic arc thrusting onto the southeasternmost south china block since 6 5 ma caused the still active taiwan orogeny the predicted accumulated deformation at present day is characterized by overall shortening onshore with contraction factors mostly between 0 8 and 1 and extension offshore with stretching factors generally between 1 and 2 the central china orogen and taiwan orogen experienced more intense shortening relative to the interior south china by factors down to 0 6 the okinawa trough experienced intense stretching by factors up to 2 5 in its central part the intraplate deformation in the south china block is closely related to the subduction of the izanagi and pacific plates the jurassic and earliest cretaceous shortening was likely induced by trench advance and the extension during the cretaceous and the cenozoic was mostly driven by subduction retreat

formation and evolution of the tancheng lujiang wrench fault system a major shear system to the northwest of the pacific ocean abstract in the northwestern peri pacific tectonic belt on the continental margin of east asia there is a series of major faults trending ne nne i e the tancheng lujiang wrench fault system this fault system extends more than 5000 km with a width of 800 1000 km in the continent and a general strike of n30 e on the basis of the results of special research on the major faults and a lot of new information about the fault system the authors discuss early mesozoic triassic jurassic period sinistral transcurrent faulting in the different regions it is suggested that in the eastern continent of east asia the e w trending tectonic pattern of the paleozoic and beginning of the mesozoic appear in the nuclei of the sino korean continent massif and the yangtze continent massif these ancient continent massifs accreted both southwards and northwards which finally led to their collision and suturing to the angura continent massif later this tectonic framework was changed greatly by the tancheng lujiang wrench fault system along which left lateral horizontal displacement of 1000 1500 km took place since the mesozoic the dislocation and deformation of horizontal displacement of the tancheng lujiang fault system produced a series of structures trending ne nne in the continental margin which have greatly transformed the ancient structures of the preceding mesozoic this is an important diktyogenese in the continent of east asia during the horizontal displacement motion of these faults the folds nappes and decollement structures pull apart basins and subductions within the continent occurred in the continent at the same time some large sinistral ductile shear zones of horizontal displacement appeared the depth of the deformed horizon of ductile shear which belongs to simple shear was controlled by the tectonic element and distance away from the continental margin whilst the ductile shear deformation occurred the fault dynamo thermal metamorphism and the fault remelting took place and magma activity appeared within the continent in the mesozoic the fault zones used to be high energy zones and recently became the seismic belts within the continent formation of the tan lu fault system was due to the collision between the southern and northern blocks its large sinistral horizontal displacement in the mesozoic was closely related to the kula plate moving northwards therefore the continent disintegrated by shearing which produced some new terranes the shear edge belt was formed between the continent and ocean the change of relative motion between the continent and pacific ocean plate transformed the tan lu fault system into first extension and then compression clarifying the characteristics of the tan lu fault system is an important key in understanding the evolution of the east asia continent since the mesozoic

progressive localization of deformation during exhumation of a major strike slip shear zone norumbega fault zone south central maine usa detailed structural studies along with 40ar 39ar thermochronology provide important constraints on the temporal spatial and structural evolution of a major orogen parallel strike slip shear zone the norumbega fault zone in maine detailed structural analysis in south central maine reveals two very different styles of dextral noncoaxial deformation a wide zone 25 km of heterogeneously distributed ductile shear structures and a relatively narrow zone 1 km of lower greenschist facies high strain mylonitization 40ar 39ar thermochronology indicates that these two zones of deformation developed during a prolonged period of regional exhumation following middle devonian amphibolite facies metamorphism the wide zone of dextral shear is interpreted to reflect a major episode of moderate temperature post amphibolite facies metamorphism but pre regional cooling below 320 c late devonian to early carboniferous transcurrent tectonism the narrow zone of dextral shear represents both a younger latest carboniferous and significantly cooler 320 c deformational event occurring at much higher structural levels a general model of increasingly narrow but more highly focused noncoaxial deformation during progressive regional exhumation is supported by the observations

40ar 39ar thermochronology of the southern gawler craton australia implications for mesoproterozoic and neoproterozoic tectonics of east gondwana and rodinia 40ar 39ar thermochronology of the southern gawler craton australia reveals a protracted history of slow cooling with local crustal heating rapid cooling and fault reactivation between 1700 and 700 ma hornblendes from most of the southern part of the craton including the kalinjala mylonite zone yield ages 1580 1610 ma with younger more discordant samples showing evidence of retrogression these results indicate that the region cooled below 500 c 100 m y after the kimban orogeny and coincident with the gawler range hiltaba suite magmatism to the north perhaps associated with postorogenic extension biotite and k feldspar data indicate that regional cooling after this time was more gradual with a few exceptions locally in the southeastern eyre peninsula rapid cooling at 1425 ma is indicated by nearly concordant hornblende and biotite ages and may record a phase of regional extension other exceptions include areas of lower grade archean rocks that cooled to 350 c by 1700 1640 ma greenschist facies reactivation of shear zones occurred at 1100 ma during the musgravian orogeny on the basis of biotite single grain data and retrogressed amphiboles k feldspar age spectra record cooling at 700 800 ma following regional intrusion of the gairdner dike swarm and or denudation during rifting along the pacific margin of east gondwana and breakup of rodinia tectonothermal events revealed by these results previous geochronological and geological studies and available paleomagnetic data are comparable to other cratons and mobile belts in australia east gondwana and laurentia providing evidence that southeastern australia and north america were adjacent during much of proterozoic time

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

dating of deformation phases using k ar and 40ar 39ar techniques results from the northern apennines abstract paleozoic to oligocene metasedimentary rocks present in the alpi apuane region of the northern apennines italy have been sequentially deformed during a tertiary progressive deformation in an attempt to date the individual deformation episodes over 50 conventional k ar and 1140 ar 39ar incremental gas release analyses have been carried out on fine grained white micas separated from samples whose structural settings were well known mineralogy x ray diffractometry and thin section analyses indicate that the constituent muscovite and phengite formed under metamorphic conditions of 3 4 kbars and 300 400 c during all deformational phases pre existing micas were variably crenulated during each subsequent deformational phase both k ar and 40ar 39ar analyses were carried out on 0 6 2 m 2 6 m and 6 20 m size separates of the phengitic white mica although the k ar apparent ages range from 11 to 27 ma and are consistent with available stratigraphic constraints the 40ar 39ar age spectra display variable internal discordancy these isotopic data indicate that 1 both the k ar and 40ar 39ar total gas ages decrease as the degree of crenulation increases 2 the k ar and 40ar 39ar total gas ages decrease as grain size decreases 3 for each sample characteristics of the 40ar 39ar age spectra depend upon grain size with fine sizes yielding discordant patterns which systematically increase in apparent age from low to high temperature and 4 phengitic micas associated with earliest structures yield generally older ages than micas associated with later structures the isotopic results are interpreted to indicate that the major deformation phase d1 occurred at approximately 27 ma with subsequent pulses ending by c 10 ma these results may be combined with finite strain data to suggest that the region was deformed at strain rates between 10 15 and 10 14 s 1 a 27 ma age indicates mid oligocene initiation of plate tectonic activity in the western mediterranean and concomitant deformation in the northern apennines

40ar 39ar and rbsr analyses from ductile shear zones from the atacama fault zone northern chile the age of deformation abstract the influence of deformation on the k ar and the rb sr isotope system is investigated it is assumed that due to the diffusion processes involved deformation has a similar effect on isotopic equilibrium as has temperature in order to examine the influence of deformation on the k ar and the rb sr isotope systems two shear zones from the atacama fault zone afz situated in the north chilean coastal cordillera have been investigated the afz which was active as a sinistral strike slip fault during the mesozoic has two sets of shear zones one formed under amphibolite sz1 one under greenschist facies conditions sz2 rb sr and 40ar 39ar age determinations were conducted on samples from cross sections of each set in sz1 the hornblendes and bioties from a weakly deformed sample reveal cooling ages of 153 152 and 150 1 ma respectively biotite from the center of the shear zone of sz1 gave an isochron of 143 9 0 3 ma mswd 0 04 which is interpreted as the age of deformation which produced resetting of the mineral system in sz2 hornblendes yielded 40ar 39ar plateau cooling ages of 138 ma biotites from undeformed samples gave rb sr and 40ar 39ar total degassing ages of 130 1 ma whereas biotite from the mylonitic rocks yielded 126 125 ma which dates the time of deformation sr isotope homogenization occurred in the mylonitic rocks and is most likely a result of deformation the formation of sz1 can be correlated to the araucanian nevadan phase the deformation in sz2 is related to the onset of uplift and cooling of the coastal cordilleran magmatic arc

40ar39ar thermochronological constraints on the structural evolution of the mesoproterozoic natal metamorphic province se africa abstract ten 40 ar 39 ar age spectra are presented for hornblende grains separated from mylonitized and weakly deformed amphibolites from the mesoproterozoic 1 2 1 0 ga natal metamorphic province nmp since the proposal of the sweat hypothesis the nmp has become a crucial area in which to study grenville aged locally termed namaquan accretion in this part of rodinia gondwana unlike many segments of the world s 1 1 ga belts the nmp is particularly suited to such studies since it is devoid of a high temperature pan african 500 ma overprint in this study we have dated hornblendes from within the earliest d1 ne directed thrust dominated structural domains of the belt the d1 domains are characterized by ne directed recumbent fold and thrust nappes and a pervasive generally s to sw dipping metamorphic foliation with down dip stretching lineations the new data constrain the minimum age of this early event which includes obduction of the northernmost tugela terrane onto the kaapvaal craton to 1135 9 ma in the d1 domains of the mzumbe terrane to the south cooling to below 550 c had only been attained by 1005 ma we also dated amphibolites from the later d2 structural domains which are characterized by sub vertical sinistral mylonite belts with sub horizontal to oblique stretching lineations our data show that d2 oblique shearing commenced at 1050 1035 ma in the mzumbe terrane and only terminated at 980 ma the youngest movements also included reactivation of major d1 structures such as the melville thrust mzumbe margate terrane boundary at 990 ma finally indications of minor pan african resetting was detected during the first 5 of the ar ar spectra from mylonites of the lilani matigulu shear zone tugela mzumbe terrane boundary indicating the polyphase nature of this major structure it has been suggested that the d1 event records the early ne sw directed arc continent collision history of the belt whilst the d2 event represents a continuation of essentially the same convergence vectors after extensive crustal thickening the new data place important time constraints on the major tectonic events in the nmp which appear comparable in many ways to other parts of the global grenvillian orogen

evidence and dynamics for the change of strike slip direction of the changle nanao ductile shear zone southeastern china abstract the changle nanao ductile shear zone was developed from a suture zone the evidence from the ductile fabrics and mylonitic microstructures indicates that the strike slip was sinistral during pre collision it became dominantly dextral in the syn collision stage in late early cretaceous the dextral strike slip movement continued in the post collision stage with extension as the dominant process the strike slip movement of the zone was strictly controlled by dynamics of collision between the fujian min taiwan tai microcontinent and the fujian min zhejiang zhe mesozoic volcanic arc during the time interval of 100 120 ma the min tai microcontinent in which the ductile shear zone developed might have been located originally to the south of its present position the northward migration of the microcontinent had contributed to a few hundred kilometers of drift rather than a shear displacement the real shear displacement is small due to the change of strike slip direction from sinistral to dextral

s wave tomography of the crust and uppermost mantle in china 1 we use 280 000 local and regional arrival times from 13 105 local earthquakes recorded by 220 seismic stations to determine a three dimensional s wave velocity structure of the crust and uppermost mantle under china and surrounding regions we use a traveltime tomography code that accommodates a heterogeneous crust and varying moho depth the grid for tomographic inversion is 1 1 in the horizontal direction and 10 km in depth our results show that large velocity variations of more than 6 exist in the crust and upper mantle in the china region the velocity image of the upper crust correlates with surface geological features crustal heterogeneity is clearly observed and velocity changes are visible across some of the large fault zones in tibet low velocities exist in the thick crust and high sn velocities exist in the southern and eastern parts low velocity zones beneath volcanic sites and the rifts are clearly observed in our tomographic results under the tengchong hainan and changbai volcanic areas strong low velocity zones are visible down to the upper mantle indicating the existence of magma chambers beneath the volcanoes

dating mylonitic deformation by the 40ar 39ar method an example from the norumbega fault zone maine strongly mylonitic rocks associated with the regionally extensive norumbega fault zone in south central maine provide an excellent opportunity for testing the effects of mylonitization on argon isotopic systems in muscovite 40ar 39ar muscovite age spectra from samples outside the zone of mylonitization are relatively undisturbed and have well defined early carboniferous plateau ages in contrast to these nonmylonitized samples all age spectra for muscovite from the mylonites are highly discordant they are characterized by young ages at low extraction temperatures which systematically increase to ages that equal the plateau ages for muscovite collected outside the mylonite zone detailed petrographic observations suggest that these systematic discordances reflect a mixing of argon components from older relict muscovite porphyroclasts and fine grained white mica aggregates that recrystallized during mylonitic deformation total gas ages of five different grain size fractions separated from the same mylonite sample become progressively younger with decreasing grain size indicating a larger component of the recrystallized grains in the finer grain size fractions although the three finest grain size fractions give different total gas ages and do not overlap in age for most of their release spectra their initial increments do coincide at approximately 290 ma this indicates a minimal older age contribution from the relict porphyroclasts in the initial increments and suggests the 290 ma age provides a good estimate for the time of mineral growth associated with mylonitic deformation these data combined with kinematic analysis reveal that the segment of the norumbega fault zone studied the sandhill corner fault is a late carboniferous early permian dextral strike slip fault a lack of significant offset in regional early carboniferous mineral age patterns across the fault suggests that displacement was probably less than 30 km this study demonstrates that 40ar 39ar dating methods can be used to date deformational events effectively as long as several important criteria are met first and foremost samples must be well characterized prior to analysis dynamic recrystallization must have occurred at or below the closure temperature of the mineral to be analyzed regional cooling patterns must also be established through detailed thermochronology so that mineral ages and age spectra from the deformed rocks can be compared to regional cooling ages of the same mineral finally the effects of excess argon must be negligible

ages of deformation from k ar and 40ar 39ar dating of white micas a structural and isotopic dating study of white micas from mylonites in the ruby gap duplex off central australia shows that mylonitic deformation occurred during the paleozoic alice springs orogeny deformation of the white micas took place under greenschist facies conditions in the approximate temperature range 250 350 c two distinct populations of white mica have been found 1 porphyroclasts of original muscovite and 2 neocrystallized phengites that define the fabric associated with deformation 40ar 39ar age spectra of neocrystallized phengites yield plateau like spectra of paleozoic age in contrast 40ar 39ar age spectra of muscovite porphyroclasts exhibit proterozoic apparent ages indicating that white micas were not open to significant argon diffusion during formation of the ruby gap duplex we conclude that the ages measured on neocrystallized phengites record the cessation of ductile deformation and migration of tectonic activity toward the internal zones of the thrust system

ductile deformation and 40ar 39ar dating of the changle nanao ductile shear zone southeastern china abstract an investigation of ductile deformation mylonitization and 40ar 39ar geochronology in the changle nanao ductile shear zone southeastern china is reported in this paper at least two phases of ductile deformation occurred in the shear zone in the mesozoic the first is a ne trending foliation widely developed in metasedimentary rocks and orthogneisses and is associated with metamorphism of amphibolite facies at 165 178 ma the second is a strike slip related ductile deformation developed both in the metamorphic rocks and the mesozoic volcanics and includes folds shear foliation or cleavage s c fabrics ne striking stretching lineation and mylonitic microstructures the ductile deformation and dislocation microstructures of quartz and the brittle deformation microstructures of plagioclase in the mylonites from the shear zone indicate that the second phase of ductile deformation and mylonitization occurred under greenschist facies conditions at temperatures of 300 350 c 40ar 39ar plateau ages of five minerals from deformed and mylonitized rocks in the shear zone are in the range of 118 107 ma the plateau ages record the time of ductile deformation and mylonitization associated with strike slip movement along the changle nanao ductile shear zone

a multidisciplinary study on the emplacement mechanism of the qingyang jiuhua massif in southeast china and its tectonic bearings part i structural geology ams and paleomagnetism during the cretaceous the south china block scb experienced a widely distributed extensional event including numerous plutons emplacement and basin opening investigations on the tectonic regime coeval with pluton emplacement and emplacement mechanism of the pluton remain relatively rare in the scb in order to address these questions a multidisciplinary approach including field structural and petrographic observations anisotropy magnetic susceptibility ams and paleomagnetic analyses was carried out on the qingyang jiuhua granitic massif which intrudes into the lower yangtze fold belt in the northeastern part of scb the qingyang jiuhua massif is composed of the granodioritic qingyang and monzogranitic jiuhua plutons dated by zircon u pb method at ca 142 ma and ca 131 ma respectively our structural observations show that the intrusion of the qingyang jiuhua massif does not modify the fold strike a weak ductile deformation of the country rocks and granitoid can be only observed in the boundary zone with limited contact metamorphism in the contact aureole of the massif the foliation follows the pluton contour and the mineral lineation is rare when present it exhibits a down dip attitude field and microstructural observations indicate isotropic magmatic textures in most parts of the massif the ams analysis of 93 sites reveals weak values for the anisotropy degree pj 0 for most of the measured samples two principal foliation patterns are identified horizontal foliations in the center of the plutons and vertical foliations on the boundaries magnetic lineation strike is largely scattered and weakly inclined at the scale of the entire massif the paleomagnetic investigations indicate that a the younger jiuhua pluton did not produce a remagnetization in the older qingyang pluton b no relative movement can be observed between these two plutons c the entire massif did not experience any important relative movement with respect to south china considering the paleomagnetic uncertainties integrating the newly obtained results with previous observations our study favors a permissive emplacement mechanism for the two plutons i e vertical magma intrusion into an opening space controlled by the nw se brittle stretching of the upper crust which is in agreement with a weak extensional regional tectonic framework of the scb

thermal and structural evolution of the intracratonic arltunga nappe complex central australia the thermal and structural evolution of a paleozoic thrust system in central australia the arltunga nappe complex has been examined through field mapping petrographic microstructural and chemical analyses k ar and 40ar 39ar thermochronology and multi diffusion domain time temperature modeling of k feldspar 40ar 39ar data the arltunga nappe complex contains three distinct tectonic units bounded by regional faults and shear zones that have undergone contrasting deformational and metamorphic histories the cooling history of the three tectonic units has been constrained by k ar and 40ar 39ar isotopic age data from k feldspars micas and amphiboles results are consistent with a piggyback history of crustal imbrication spanning over 100 m y with the hottest rocks uplifted and cooled first and with imbrication acting progressively toward the foreland implications for the intracratonic paleozoic tectonics of central australia are 1 uplift within the structurally highest tectonic unit was initiated before 400 ma 2 continued piggyback imbrication footwall failure and uplift and exhumation of the crust resulted in duplexing in the lowest structural unit at approximately 325 300 ma 3 the contrast in thermal history between the tectonic units indicates that once widely separated crustal segments were juxtaposed during thrusting above a hinterland dipping megathrust resulting in 85 km of crustal shortening

post orogenic thermal reset of the pingtan dongshan metamorphic belt se china insights from zircon fission track and u pb double dating abstract zircon double dating technique for u pb and fission track ft ages is used to reassess the cooling conditions for the pingtan dongshan metamorphic belt pdmb three cretaceous gneissic bodies from the chinmen area and two dioritic plutons from the zhangzhou igneous complex zic in two sides of the changle nanao fault are studied u pb dating results define the magma emplacement of gneisses at 144 134 ma and dioritic rocks at 102 99 ma and ft dating results give ages of 96 86 ma and 87 ma for corresponding samples combining 40ar 39ar mineral ages reported previously the fast cooling curve 86 c myr 100 96 ma of zic plutons matches near surface intrusives however those for deep seated chinmen gneisses are problematic as their resultant conditions are similar to zic samples a recent concept favors the early to late cretaceous tecto magmatic evolution in the coastal se china involving episodes of orogenic magmatism 147 130 ma and shallow magmatism under post orogenic extension 110 85 ma as the pingtan island in northern pdmb is considered as a remnant piece of colliding fragment the cooling rate known for gneissic bodies in this island 35 c myr 130 120 ma can better represent the record of this collision on the basis of these features we advocate a magmatic quiescence at 130 120 ma representing collision between pdmb and a concealed microcontinent which resulted in rapid uplift of this metamorphic belt cooling curves obtained for chinmen gneisses are suggested to have further subjected to thermal reset by high temperature magmatism taking place during the post orogenic stage

a broadband p wave analysis of the large deep fiji island and bolivia earthquakes of 1994 the complex broadband p wave displacement recordings of the 570 km deep march 9 1994 mw 7 6 fiji island and the 660 km deep june 9 1994 mw 8 2 bolivia earthquakes are analyzed to estimate the spatial and temporal characteristics of their ruptures we model relative arrival times and amplitudes of coherent subevents in p waveforms and perform waveform analyses we resolve 1 short rupture durations relative to their seismic moments 12 and 40 s for the fiji and bolivia earthquakes respectively 2 small areas of main moment release for both earthquakes 30 40 km 3 high stress drops compared to shallow earthquakes with the stress drop of the bolivia event 283 mpa being significantly higher than the stress drop of the fiji event 26 mpa 4 small changes in mechanism up to 10 changes in fault plane orientation and 5 a steeply dipping rupture plane for the fiji earthquake and a shallowly dipping rupture plane for the bolivia earthquake details of the ruptures are difficult to resolve using teleseismic p waveforms

the late cretaceous tectonic evolution of the south china sea area an overview and new perspectives from 3d seismic reflection data abstract the late cretaceous is a significant geologic period in the south china sea area as it marks the tectonic transition from the early paleo pacific plate subduction to the subsequent cenozoic rifting related to the opening of the scs however the late cretaceous tectonic evolution of the south china sea area is yet to be clearly defined and it is at present largely debated in the literature in this paper mainly on the basis of 240 000 km2 newly acquired 3d seismic reflection data 94 industrial wells and existing u pb ages of basement granitoids we carried out an integrated interpretation mapping and analysis of the pre cenozoic 66 ma structures within the basement of the cenozoic rift basin in the northern south china sea area that can be crucial for a broad understanding of the late cretaceous tectonic evolution of this region results of this analysis suggest that three late cretaceous fault systems can be identified in the northern south china sea margin 1 the wnw striking thrust system 2 ene striking extensional fault system and 3 ene striking thrust system these three fault systems are considered to have developed in the late cretaceous since they are superimposed on the well dated late jurassic to early cretaceous 161 6 101 7 ma arc related granitoids that define most of the basement of the cenozoic rift basin within the study area this new structural evidence combined with a review of previous studies led us to propose a renewed multi phase geodynamic evolutionary model of the south china sea area during the late cretaceous the first tectonic event that can be recognized generated the wnw striking thrust system and is in this paper interpreted to have formed as a result of a sinistral transpressional event that took place in the south china sea area and adjacent areas around 100 ma at the early late cretaceous boundary this transpressional event was likely related to intense oblique convergence between the paleo pacific ocean plate and the eurasia plate the second tectonic phase that was identified in this paper 100 ma to 72 ma is defined by an extensional event that generated the largely ene striking extensional fault systems and associated basins which is interpreted to be related to the back arc extension that took place in this period in response to the slab roll back and high angle subduction of the paleo pacific plate this extensional phase eventually led to the opening of the proto south china sea on the se margin of the proto south china block and it should be distinguished from the cenozoic rifting phases that are related to the opening of the south china sea the third and last tectonic phase that was recognized in this paper is a compressional event that took place in the late stage of the late cretaceous 72 ma to 66 ma and was responsible for the development of the ene striking thrust system we suggest that this post subduction post yanshanian compressional event can be interpreted to have developed in response to process of ridge push related to the sea floor spreading of the proto south china sea

rifting and reactivation of a cretaceous structural belt at the northern margin of the south china sea abstract the tiu tang lung fault hong kong special administrative region china is located on the northern stretched continental margin of the south china sea along this fault middle jurassic volcanic rocks of the tai mo shan formation are tectonically juxtaposed on lower cretaceous sedimentary rocks of the pat sin leng formation both extensional detachments and compressional features are observed and various genetic strain configurations are proposed for the tiu tang lung fault with implications for understanding the dynamics of the pre south china sea rifting during the cretaceous we have identified tilted bedding planes in the continental deposits of the pat sin leng formation which can be related to early cretaceous syn extensional deposition a mid cretaceous penetrative top to the south to top to the west shear fabric is also observed and serves as an indicator of the strain pattern this deformation is expressed by cleavages schistosity s c fabrics kink folds phacoids and stretched pebbles at both a macroscopic and microscopic scale cleavages and bedding are generally sub parallel to the local shear orientation the whole sedimentary pile is crosscut by cenozoic n70 and n150 normal faults these constraints together with previous fission track seismic and structural data allow us to reinterpret the kinematics of this domain during syn orogenic to syn extensional periods the observed top to the south thrusting event is coeval with ne sw strike slip sinistral fault movement subsequent n s extension can be correlated with south china sea rifting from eocene to oligocene these observations reveal a polyphase history associated with continental margin inversion which witnessed localized extension on previous compressional structures

structural evolution and 40ar 39ar dating of the zanhuang metamorphic domain in the north china craton constraints on paleoproterozoic tectonothermal overprinting abstract the zanhuang domain in the hinterland of the north china craton consists of archaean paleoproterozoic mesoproterozoic and palaeozoic rocks and was previously considered a mesozoic metamorphic core complex our reappraisal of regional structural history and mineral 40 ar 39 ar geochronology shows that the domain was subjected to a number of deformation events and had a heterogeneous uplift cooling history during the paleoproterozoic four primary deformation events have been recognized in the domain the first event reflects the earliest deformation in the region however only closed and rootless folds are preserved d2 was dominated by wnw ese shortening and top to ese thrusting in a collisional environment d3 was a divergent extensional and ductile shearing event driven by the post collisional extensional collapse and exhumation of the thickened crust in the domain d4 was characterized by localized ductile shearing with the development of three nne trending ductile shear zones the 40 ar 39 ar plateau ages derived from the thermochronology analyses of the biotite concentrates from the metamorphic rocks are interpreted as cooling ages through biotite 40 ar 39 ar closure temperature 300 c and this allows us to constrain the timing of deformation events in conjunction with the evidence from structural analyses and previous geochronological data we conclude that 1870 and 1870 1826 ma define the timing of d1 and d2 events respectively while 1826 1793 ma represents the age of d3 the last event d4 occurred at 1689 1633 ma as constrained by 40 ar 39 ar plateau ages of biotite concentrates from the mylonites within the ductile shear zones these data together with k feldspar 40 ar 39 ar geochronology allows us to depict the cooling history of the region during the paleoproterozoic and mesoproterozoic it appears that the uplift cooling rate varies temporally and spatially in the region

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

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

retrograde evolution of eclogites evidences from microstructures and 40ar 39ar white mica dates munchberg massif northern bavaria phengites from eclogites and pegmatites 3t 2m1 coarse grained and recrystallized of the munchberg massif weissenstein and oberkotzau have been dated by the 40ar 39ar method 3t micas from the eclogites yielded plateau and isochron ages of 365 7 ma 2m1 micas show disturbed degassing spectra micas from pegmatites show a slight excess ar component with an isochron age of 353 to 351 3 ma an age component of approximately 300 ma was also detected in combination with age values from the literature the cooling history of the munchberg massif from eclogite facies conditions 390 ma to cooling below 350 c 350 ma is documented the age component of 300 ma is attributed to a low grade stage of mineral growth accompanied by a transitional ductile brittle deformation the petrological effects include formation of pumpellyite prehnite facies minerals frequently precipitated in microcraks and cleavage planes of earlier formed minerals this stage has to be seen in conjunction with the intrusions of the fichtelgebirge granite

early mesozoic thrust tectonics of the northwest zhejiang region southeast china the nw zhejiang region of south china occupies a key tectonic position near the suture zone of the yangtze and cathaysian blocks and is of critical importance for the assembly of east asia sedimentological and tectonic analyses indicate that the region had a se dipping paleoslope in the late paleozoic to early triassic a transitional sedimentary environment from deep sea to continental molasse is documented in the early triassic late triassic interval associated structures are nw vergent folds and thrusts that root southeastward beneath the high grade chencai metamorphic complex the structural styles of this foreland fold and thrust belt are characterized by multifold duplexes and individual folds that are together zoned from se to nw as follows 1 core zone characterized by shear folds and ductile thrusts 2 se belt with out of sequence thrusting of multifold duplexes and an average shortening of 50 3 central belt with duplexes imbricate fans and an average shortening of 40 and 4 nw belt with jura type folds and a shortening of 10 a tectonic model for the foreland fold and thrust belt is discussed in relation to the early mesozoic archipelago paleogeography of south china

deformation of granitoid plutons in the dongshan area southeast china constraints on the physical conditions and timing of movement along the changle nanao shear zone the ne trending changle nanao shear zone has affected several granitoid plutons in the dongshan area southeast china microstructures in the granitoids range from undeformed to solid state lineations and foliation migmatitic textures are common in some units microprobe analysis of total al has been carried out on hornblende rims in four samples of gneiss from various points across the shear zone confining pressures calculated fall into range of 4 2 4 9 kb the average pressure 4 5 kb suggests that the shear zone may have reached at least 16 km depth fluid inclusion studies referred from the correspondent p t isochores indicate that the temperature of ductile deformation in the shear zone was 740 c observations on intrusive relations between the various granitic phases and their relative degrees of deformation suggest that emplacement of the different magma phases may be closely related in time and to movement along the changle nanao shear zone zircon from one deformed pluton yielded a crystallization u pb age of 121 5 2 8 ma field and microstructural data suggest the dated pluton is syntectonic which constrains the upper age of high temperature deformation in the orthogneiss along the changle nanao shear zone at that locality

early cretaceous tectonostratigraphic evolution of the erlian basin ne china a record of late mesozoic intraplate deformation in east asia abstract the erlian basin is one of the largest intracontinental meso cenozoic basins in northeast china the basin is filled with extra thick cretaceous sediments and offers unique opportunities to untangle the late mesozoic intraplate deformation in east asia however despite decades of petroleum exploration in the basin the early cretaceous chronostratigraphy and structural evolution of the erlian basin have been poorly studied based on newly obtained zircon u pb geochronological data well lithological logs and seismic reflection profiles the present study carries out a detailed analysis of the tectonostratigraphic evolution of the erlian basin during the early cretaceous the depositional ages of the lower cretaceous strata in the basin are refined and the early cretaceous evolution of the basin is reestablished the lower aershan upper aershan lower tenggeer upper tenggeer and saihan formations are constrained to the middle valanginian ca 138 135 ma late valanginian ca 135 133 ma hauterivian early aptian ca 133 121 ma middle aptian ca 119 115 ma and latest aptian albian post ca 115 ma respectively the early cretaceous syn rift subsidence of the basin was intermittent rather than continuous and was punctuated by multiphase contractional deformation during the earliest cretaceous prior to ca 138 ma middle valanginian ca 135 ma latest valanginian ca 133 ma middle aptian ca 120 ma late aptian ca 115 ma and early late cretaceous boundary we tentatively attribute the extensional and contractional deformation in the erlian basin to a series of continental collisions along asian margins karakoram lhasa qiangtang collision kolyma omolon siberia collision siberia amuria collision chukotka kolyma omolon collision west philippines south china collision and okhotomorsk east asia collision

mesozoic tectonic evolution of the southeast china block new insights from basin analysis abstract in order to better understand the mesozoic tectonic evolution of southeast china block secb in short this paper describes geological features of mesozoic basins that are widely distributed in the secb the analyzed data are derived from a regional geological investigation on various mesozoic basins and a recently compiled 1 1 500 000 geological map of mesozoic cenozoic basins two types of basin are distinguished according to their tectonic settings namely the post orogenic basin type i and the intracontinental extensional basin type ii the latter includes the graben and the half graben or faulted depression basins our studies suggest that the formation of these basins connects with the evolution of geotectonics of the secb the post orogenic basin type i was formed in areas from the piedmont to the intraland during the interval from late triassic to early jurassic and the formation of the intracontinental extensional basin type ii connects with an intracontinental crustal thinning setting in the late mesozoic the graben basin was generated during the middle jurassic and is associated with a bimodal volcanic eruption and the half graben or faulted depression basin filled mainly by the rhyolite tuff and sedimentary rocks during early cretaceous is occupied by the late cretaceous paleogene red colored terrestrial clastic rocks we noticed that the modern outcrops of numerous granites and basins occur in a similar level and the mesozoic granitic bodies contact with the adjacent basins by large normal faults suggesting that the modern landforms between granites and basins were yielded by the late crustal movement the modern basin and range framework was settled down in the cretaceous abundant sedimentary structures are found in the various basins from that the deposited environments and paleo currents are concluded during the late triassic early jurassic time the source areas were situated to the north and northeast sides of the outcrop region in this paper we present the study results on one geological and geographical separating unit and two separating fault zones the wuyi orogenic belt is a late mesozoic paleo geographically separating unit the ganjiang fault zone behaves as the western boundary of early cretaceous volcanic rocks and the zhenghe dapu fault zone separates the se china coastal late mesozoic volcanic sedimentary basins and the wuyi orogenic belt finally we discuss the geodynamic mechanisms forming various basins proposing a three stage model of the mesozoic sedimentary evolution

alpine deformation and 40ar 39ar geochronology of synkinematic white mica in the siviez mischabel nappe western pennine alps switzerland we explore the timing of deformation and exhumation of the siviez mischabel nappe western swiss alps which has been considered a classic example of a midcrustal crystalline nappe since the studies of argand 1916 this study presents 40ar 39ar ages obtained on both synkinematic white mica from permo triassic cover sediments and more complex white mica populations from basement gneisses of the siviez mischabel and middle pennine nappes primary foliation developed in cover units by nucleation growth and rigid rotation of mica grains during noncoaxial alpine deformation although some samples show a crenulation of this primary foliation mica growth appears to have occurred only during the development of primary foliation the main phase of greenschist facies deformation related to imbrication of the siviez mischabel nappe and other middle pennine nappes good agreement exists between independent estimates of the timing of deformation and reported 40ar 39ar white mica ages from cover units of the central and southern siviez mischabel nappe in cover units from the central and southern siviez mischabel regions of the study area 40ar 39ar ages appear to date synkinematic white mica growth results suggest that the siviez mischabel nappe was emplaced and developed foliation during a 5 m y period from 41 to 36 ma in cover units from the eastern siviez mischabel however 40ar 39ar white mica ages appear to date postkinematic thermal events these thermal events may be related to oligocene magmatic activity in the lower pennine nappes or to miocene development of the simplon fault zone variations in the relation between alpine age and grain size for cover samples from the central eastern and southern siviez mischabel correlate well with the regional variations in temperature inferred from quartz microfabrics and the pattern of regional metamorphism when considered in concert with other recent isotopic studies on the timing of major tectonic and thermal events in the western swiss alps these data support arguments that the relative timing of events such as thrusting and back thrusting of crystalline nappes in hinterland units and exhumation of high pressure units in the suture zone of the western alps are intimately related and synchronous on the scale of a few million years

cretaceous cenozoic history of the southern tan lu fault zone apatite fission track and structural constraints from the dabie shan eastern china apatite fission track aft and structural data outline the late cretaceouscenozoic history of the southern tan lu fault zone tlfz one of asia s major faults the triassic jurassic dabie orogen earth s largest track of ultrahigh pressure rock exposure and its foreland the yangtze foreland fold thrust belt the fission track analyses utilized the independent z and n methods for age determination which yielded within error identical ages ages from triassic jurassic syn orogenic foreland sediments are younger than their depositional age and thus were reset a group of ages records rapid cooling following shallow emplacement of granitoids of the widespread latest jurassicearly cretaceous yanshanian magmatism most ages are 90 to 55 ma and document cooling following reheating at 110 90 ma the time when the basement units of the dabie shan were last at 200 jc this cooling coincides with rifting marked by the late cretaceouseocene red bed deposition in eastern china during this period the dabie basements units exhumed in the footwall of the tan lu fault with the qianshan basin in the hanging wall the associated stress field is transtensional nw trending principal extension direction the youngest fission track ages and temperature time path modeling point to enhanced cooling in the footwall of the tan lu and associated faults at 45f10 ma the related stress field is transtensional with the principal extension direction changing trend from nw to w it may be the far field expression of the india asia collision superposed on the back arc extension setting in eastern china a regional unconformity at f25 ma marks an upper bound for the inversion of the late cretaceouseocene rift structures during the neogene further subsidence in the eastern china basins was accommodated by sub horizontal ne sw extension and followed by the presently active nw se extension the tan lu fault along the eastern edge of the dabie shan had normal

the timing of and nature of greenschist facies deformation and metamorphism in the upper pennine alps the upper pennine nappes in the western alps are cut by structures that locally place european basement rocks over those of the piemonte zone which represent the sutured remains of alpine ocean crust in the taschalp area of switzerland the mischabel backfold and associated se verging shearing carries gneisses of the grand saint bernard nappe over eclogitic material of the zermatt saas zone greenschist facies assemblages are developed locally in the foot wall and hanging wall of the mischabel structure as well as in the sheared rocks of the thrust zone rb sr 40ar 39ar and u pb studies of white micas amphiboles and sphenes show that greenschist assemblages developed at circa 44 ma in the zermatt saas zone of the footwall and at circa 40 ma in the thrust zone rb sr data from the literature document muscovite and biotite ages in strongly foliated grand saint bernard gneisses of the hanging wall of circa 36 and 32 ma respectively these are thought to indicate that deformation on the mischabel structure continued for at least 5 m y rapid cooling inferred for the zermatt saas ophiolites in the mid eocene may document either the tectonic emplacement of the ophiolite over the underlying monte rosa massif or their extensional unroofing it is not possible to determine with certainty whether the mischabel structure is extensional or contractional on a crustal scale the age of cooling and deformation reported here show that it is not possible that the mischabel structure was responsible for the exhumation of the high pressure assemblages in the zermatt saas and monte rosa rocks

diachronous variscan tectonothermal activity in the nw iberian massif evidence from 40ar 39ar dating of regional fabrics abstract multigrain concentrates of hornblende and muscovite together with whole rock slate phyllite samples have been dated 27 analyses using 40ar 39ar incremental release methods along a systematic traverse across the various lithotectonic structural elements which comprise northwestern sectors of the variscan iberian massif hornblende concentrates from amphibolites in the allochthonous ordenes complex yield plateau isotope correlation ages of 425 ma and 377 ma muscovite concentrates and whole rock slate phyllite from this and the cabo ortegal complex yield plateau ages which range from 367 ma to 295 ma analyses of similar material from the relative autochthon yield plateau ages between 359 ma and 275 ma muscovite concentrates from three late to post kinematic granitic stocks yield plateau ages between 309 ma and 274 ma at least seven of the 40ar 39ar analyses from metamorphic rocks record variable thermal rejuvenation of intracrystalline argon systems associated with emplacement of proximal granitic stocks the remaining analyses may be used to constrain the local age of various variscan tectonothermal events the oldest fabric ages are recorded in allochthonous units whereas the youngest fabric ages occur along the boundary between internal and external zones middle devonian ages are recorded in the allochthon and suggest a chronological continuity with deformational events in the relative autochthon where variscan deformation initiated in the upper devonian and diachronously prograded eastward the first deformational events recorded in the limit within the internal and external zones occured ca 20 25 ma later lower namurian variscan deformation systematically prograded diachronously eastward across the orogen as new crustal material was added along the front of the developing orogenic wedge however the entire orogen remained tectonically active with different structural features forming at different times and at different places an average propagation rate of ca 5 km m y is suggested by consideration of a 20 25 ma difference in correlative fabric ages and present separations

synorogenic extension quantitative constraints on the age and displacement of the zanskar shear zone northwest himalaya structural thermobarometric and geochronological data place limits on the age and tectonic displacement along the zanskar shear zone a major north dipping synorogenic extensional structure separating the high grade metamorphic sequence of the high himalayan crystalline sequence from the overlying low grade sedimentary rocks of the tethyan himalaya a complete barrovian metamorphic succession from kyanite to biotite zone mineral assemblages occurs within the 1 km thick zanskar shear zone thermobarometric data indicate a difference in equilibration depths of 12 3 km between the lower kyanite zone and the garnet zone which is interpreted as a minimum estimate for the finite vertical displacement accommodated by the zanskar shear zone for the present day dip of the structure 20 a simple geometrical model shows that a net slip of 35 9 km is required to regroup these samples to the same structural level because the kyanite to garnet zone rocks represent only part of the zanskar shear zone and because its original dip may have been less than the present day dip these estimates for the finite displacement represent minimum values field relations and petrographic data suggest that migmatization and associated leucogranite intrusion in the footwall of the zanskar shear zone occurred as a continuous process starting at the barrovian metamorphic peak and lasting throughout the subsequent extension induced exhumation geochronological dating of various leucogranitic plutons and dikes in the zanskar shear zone footwall indicates that the main ductile shearing along the structure ended by 19 8 ma and that extension most likely initiated shortly before 22 2 ma

tracing an early jurassic magmatic arc from south to east china seas drilling has revealed suites of magnesian granite and diorite emplaced in early jurassic time 198 195 ma and an arc related low temperature 678 to 696 c magmatism in ne south china sea these rocks have 87sr 86sri 0 705494 to 0 706623 and endt 0 9 to 2 2 as evidence of evolved mantle derived magmas coupled with enriched fluid mobile elements cs to k and pb implying involvement of subduction zone fluids another early jurassic granodiorite zircon u pb 187 ma drilled from the sw east china sea is a magnesian high k calc alkaline is comparably confined to a range of low temperature 675 c arc related granite characterized by enrichment of fluid mobile elements and nb ta depletion its sr nd isotopes 87sr 86sri 0 705200 endt 1 1 suggest a product of evolved mantle derived melts together with detrital igneous zircons from paleocene sequences these observations reveal an early jurassic arc related low temperature 600 to 740 c magmatism in the sw east china sea these arc related granitoids along with those from se taiwan could define an early jurassic ne sw trending dongsha talun yandang magmatic arc zone along the east asian continental margin paired with jurassic accretionary complexes from sw japan e taiwan to the w philippines this arc subduction complex assembly was associated with oblique subduction of the paleo pacific slab beneath eurasia presumably responsible for early jurassic lithospheric extension in south china block

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