seismicity normal faulting and the geomorphological development of the gulf of corinth greece the corinth earthquakes of february and march 1981 three major destructive earthquakes of m s 6 7 6 4 6 4 occurred in the eastern part of the gulf of corinth in february and march 1981 associated normal faulting was observed on both the north and the south sides of the gulf examination of teleseismic local seismic surface faulting and geomorpbological data suggests that the first and second of these shocks activated major north dipping normal faults these faults control the topography and bathymetry and are related to the recent uplift and subsidence of the coastline it is probable that the first earthquake occurred on a faultwhich outcrops underwater and the second on a fault which is visible on land it appears that the third shock activated an antithetic normal fault dipping southwards on the north side of the gulf and that the overall structure of the gulf of corinth graben is asymmetric the northern antithetic fault clearly demonstrates the geomorphological changes associated with developing young normal faulting in addition we suggest that observations of recent coastline movement provide a powerful tool for identifying major active fault systems and predicting their historical role in the paleogeography of an area

influence of pre existing pervasive fabrics on fault patterns during orthogonal and oblique rifting an experimental approach abstract pervasive mechanical anisotropy e g metamorphic foliation in the pre rift basement rocks often appears to control the orientation of new faults in natural rift systems and thus tend to influence formation of fault bounded sedimentary basins however the extent to which this influence works in nature has remained debatable and contrasting ideas exist regarding the issue of structural inheritance in natural rifts like the east african rift system earlier experimental works have investigated different kinematic aspects of faulting in simulated orthogonal and oblique rift systems including the role of a crustal scale pre existing zone of weakness on continent scale rifting these experiments have tested the influence of discrete pre existing weak zones e g pre existing faults or an ancient orogenic belt on localization of subsequent rifting but have not considered the control of pervasive fabric anisotropy e g metamorphic foliation etc in pre rift basement rocks on the fault patterns during rifting here we present a series of simple roughly scaled analog model experiments where pervasive strength anisotropy in the basement was created by brushing plaster of paris on a viscous pitch substratum this way a transverse anisotropy of tensile strength was generated in the plaster of paris layer due to thickness variation across the brush marks the basement was overlain by a dry sand pack simulating weak sedimentary rocks overlying a foliated crystalline basement orthogonal and oblique extension of the models at various angles and with differently oriented strength anisotropy exhibited the control of the anisotropy on the orientations of new faults in the sand layer in general anisotropy could significantly control the fault pattern only when it was at a high angle 45 with respect to the maximum instantaneous horizontal stretching direction e h1 otherwise they largely disregarded the anisotropy and formed orthogonal to e h1 faults never formed orthogonal to the displacement vector d in oblique rifting unless the fault controlling anisotropy was perpendicular to d faults strongly following the anisotropy were much longer than those not following that trend faults oblique to the anisotropy were short segmented and tortuous in nature and mainly grew by segment linkage the experimental results support many field observations made in the east african rift system and are likely to be applicable to other rift systems like gondwana basins of india where field data on such structural inheritance are meager

multistage structural deformations of a superimposed basin system and its tectonic response to regional geological evolution a case study from the late jurassic early cretaceous tanan depression hailar tamtsag basin abstract the spatial temporal extent and influence of the mongol okhotsk and paleo pacific tectonic regimes in northeast ne china and adjacent areas during late mesozoic times have long been controversial as a superimposed rift system which formed due to extensive intracontinental extension during the late jurassic to early cretaceous periods the hailar tamtsag basin is a key area to study the relationship between the mongol okhotsk and paleo pacific tectonic regimes and their superposition with the aim of constraining the evolution of those two regimes in this paper the tanan depression which is a second order structural unit in the western part of the hailar tamtsag basin has been chosen as the research object on the basis of structural analysis of three dimensional 3d seismic data in the tanan depression and taking into account the controlling effect and influence of the pre existing facies on the basin evolution the deformation events in the early cretaceous can be subdivided into four periods 1 a nw se trending extension during the deposition of the tongbomiao formation to the upper part of the second member of the nantun formation 2 a nw se trending compression during the deposition of the upper part of the second member of the nantun formation to the first member of the yimin formation 3 a near ew trending extension during the deposition of the second member to the lower part of third member of the yimin formation 4 a near ew trending compression during the deposition of the upper part of the third member of the yimin formation additionally we identify compressional structures in the basement in the southeast part of the depression which is a key study that resulted from the mongol okhotsk collisional orogeny during the late jurassic the above five major deformational events make up a relatively complete tectonic deformation sequence of the hailar tamtsag basin moreover the deformation sequence together with other available information from the literature in ne china and adjacent areas including petrology geochemistry and geochronology data also record the whole process from the orogenic stage after the closure of the mongol okhotsk ocean over the post orogenic collapse of the mongol okhotsk orogen to the weakening of the influence of the mongol okhotsk regime and eventually to be replaced by the paleo pacific tectonic regime considering that the superposition and transformation of the two tectonic regimes involves almost all the geological process in ne china and adjacent area during the late mesozoic the complete geological record in the tanan depression during this period provides new constraints on the research of regional tectonic evolution and the model of multiphase deformation is also expected to have useful implications for future studies of complex basin systems

microseimicity and strain pattern in northwestern greece during a 7 week microearthquake experiment conducted in epirus akarnania and the ionian islands of western greece we located approximately 600 earthquakes with magnitudes between 2 and 4 2 no event was deeper than 40 km the seismicity cannot be clearly associated with any single fault except the lixourion right lateral fault located west of the ionian islands focal mechanisms of about 100 earthquakes show for a narrow band of earthquakes located along the coast ene wsw shortening consistent with the surface tectonics farther east focal mechanisms show nnw sse extension beneath the foothills of the pindus mountains which is unrelated to surface faulting but is consistent with the presently subsiding basins this strain pattern is seen far north and south of the lixourion fault and is similar to the one observed in the peloponnese it suggests that a large scale mechanism is responsible for the recent geodynamics of both the northwestern and southwestern aegean

bed by bed fold growth by kink band migration sant llorenc de morunys eastern pyrenees ahstract rowth strata deposited over and against the flank of the sant llorenc de morunys fold during its final stages of deformation have been mapped at high resolution as the basis for unraveling the kinematics of fold growth we use restoration techniques based on normal balancing assumptions to decipher the detailed kinematic history of folding the progressive restorations as well as balanced forward modeling show that the last few hundred meters of fold growth were dominated by kink band migration of a sort that is typical of much faultrelated folding the kink band migration has produced complex anticlinal hinge zone geometry including segmented fold hinges linked by disconformities and unconformities which has direct and detailed explanation in terms of fluctuations in deposition rate relative to curved hinge kink band migration rate large fluctuations in the convolution of non steady sedimentation and deformation are demonstrated although the absolute fluctuations in deformation and sedimentation are unknown at a length scale of 100 m kink band migration with little or no deposition is interspersed with sedimentation with little or no deformation at the length scale of 500 m deposition ranges from 200 to 50 of uplift 0 1997 elsevier science ltd all rights reserved

reactivation tendency analysis a theory for predicting the temporal evolution of preexisting weakness under uniform stress state abstract understanding the mechanical controls on reactivation of preexisting weakness is a fundamental problem in tectonic studies in this study we develop a theoretical framework for evaluating the likelihood of seismicity on active faults and the sequence of reactivation of multiple sets of preexisting weakness our analysis overcomes the restrictions of the early work that assumes uniform coefficient of friction across all preexisting planes with negligible cohesive strength and vertical or horizontal orientations of principal stresses using a coordinate system transformation we developed a new graphical technique that can express the reactivation problem in the mohr space with the principal stresses oriented neither vertically nor horizontally we verified the predicted sequence of reactivation on preexisting weakness and initiation of new fractures according to the byerlee law and the coulomb fracture criterion by conducting a simple sandbox experiment our proposed reactivation tendency analysis can be expanded to evaluate the likelihood of seismicity on a single fault with curvi planar geometry e g listric normal faults ramp flat thrusts and strike slip faults with restraining and releasing bend geometry our analysis also provides a new insight into the mechanical cause of temporal evolution of pre existing weakness in geologic records finally our work implies that the sequence of faulting reactivated from preexisting weakness provides critical information on the mechanical properties of the deforming lithosphere

a new model for the dynamic evolution of chinese lithosphere continental roots plume tectonics abstract chinese continental lithosphere comprises three tectonic domains 1 eastern china a region characterized by rifting extensional basins and voluminous basaltic volcanism 2 central china a plexus of cratonic terrains with low heat flow 40 50 mw m2 including the tarim erdos and yangtze blocks welded by pre cenozoic orogenic belts and 3 western china a region comprising the qinghai tibet himalaya orogen the relatively thin crust 35 km and lithosphere 70 km of eastern china is believed to reflect mantle upwelling while near normal crust 45 km and thickened lithosphere 200 km in central china suggest a mantle lithosphere root resembling those inferred for the kaapvaal and siberian cratons thickened crust 70 km and lithosphere 150 km in western china reflect the advanced development of an orogen root the lower density and relative buoyancy of central cratonic mantle roots appear to have contributed to the long term tectonic stability of the central chinese lithospheric blocks in contrast gravitational instability produced by thickening of the denser western chinese lithosphere and the resulting subsidence and eventual delamination of orogenic roots are believed to have led to postorogenic extensional collapse although the geological relationships suggest compressional forces caused both mountain building and orogen root development extensional stress resulting from gravitational collapse is believed to have induced lithospheric and crustal thinning with concomitant reduction of topography the term continental roots plume tectonics has been adopted to describe the configuration and dynamic condition of subcontinental lithosphere and upper mantle beneath china accordingly it is proposed that supracrustal tectonic forms represent the surface expressions of and responses to deep continental roots plume tectonics while the prevailing view is that the western orogenic belt is not genetically related to eastern continental rifting such a relationship is inherent to the continental roots plume tectonics model it is further proposed that the formation of orogenic lithosphere roots triggered eastward extrusion of the asthenosphere along the 400 km depth mantle interface and in response to subduction at the eastern margin produces plume like upwelling beneath eastern china we suggest that processes involved in continental roots plume tectonics are directly responsible for the formation and evolution of the eurasian supercontinent

extensional fault bend folding and synrift deposition an example from the central sumatra basin indonesia we describe an analytical method for interpreting the geometry and structural history of asymmetric half grabens in rift basins with extensional fault bend fold theory using seismic reflection profiles from the central sumatra basin and balanced forward models we show how local variations in tectonic subsidence relative to deposition rates yield distinctive patterns of folded synrift strata and unconformities that record basin history if the deposition rate exceeds the local subsidence rate folded growth strata form upwardly narrowing kink bands that have been described previously as growth triangles in contrast if the deposition rate is less than or equals the local subsidence rate growth strata are folded and truncated at the surface on half graben margins subsequent increases in deposition rate relative to subsidence rate form angular unconformities near the half graben margins these unconformities develop without the necessity of erosion and are folded by continuing fault slip strata above and below the unconformities are concordant in the deeper parts of the half grabens thus angular unconformities on half graben margins are helpful for defining sequence boundaries that may reflect changes in deposition and tectonic subsidence rates in addition fault bend fold interpretations yield fault geometry and measures of horizontal extension both of which control three dimensional half graben geometry copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received april 4 1995 revised manuscript received june 4 1996 final acceptance october 23 1996 2texaco exploration and production technology dept 3901 briarpark houston texas 77042 3pt caltex pacific indonesia rumbai pekanbaru 28271 indonesia we thank hongbin xiao and john suppe for helpful insights into their extensional fault bend fold theory which provided the foundation for this work exceptional reviews by m scott wilkerson and walter f dula jr improved the manuscript in addition discussions with karsani aulia richard e bischke peter a brennan chris d connors paul w genovese tom l heidrick and elizabeth a lorenzetti provided insights into our structural interpretations and presentation of the theory seismic reflection data were provided by pt caltex pacific indonesia

the 1978 earthquake sequence near thessaloniki northern greece summary this paper presents a detailed study of teleseismically and locally recorded foreshocks and aftershocks of the 1978 thessaloniki earthquake sequence and discusses the relations between the locations and mechanisms of these shocks and the three dimensional geometry of faulting in the source region sixteen teleseismically recorded events were relocated using a relative relocation method and positioned geographically using the accurate locally determined location of the largest aftershock all these shocks had depths shallower than 15 km the spatial distribution of the foreshocks showed that the activity was initiated at the central part of the epicentral region progressed westwards and for about 20 days clustered in the region of the imminent mainshock no teleseismically recorded foreshock was located west of the mainshock location in less than 1 hr after the mainshock large aftershocks occurred west of it and in later stages spanned the entire western part of the epicentral region no teleseismically recorded aftershocks were located east of the mainshock locally recorded aftershocks were accurately located and provided a more detailed picture of the seismic deformation they occurred at depths between 3 and 12 km and in three distinct clusters separated by well defined gaps the largest foreshock on may 23 had a moment of 5 6 1024dyne cm and a mean displacement of 31cm the mainshock on june 20 had a moment of 5 2 1025dyne cm a strain drop of 4 0 10 5 static stress drop of 12 bar and a mean displacement of 64 cm these values are for one of the two possible interpretations of the aftershock distribution which suggests that the largest earthquakes of the sequence occurred on two different but adjacent fault segments the first event 1 on may 23 occurred along the central fault segment and was followed 28 days later by the second event 2 on june 20 along a western fault segment finally 61 days later another smaller earthquake event 3 occurred along another fault east of event 1

seismotectonics and the earthquake frequency magnitude distribution in the aegean area summary a study of aegean seismotectonics and the resulting frequency magnitude distribution on a broad scale is undertaken using the tectonic model of le pichon angelier this implies a tectonic moment release rate due to the spreading of the aegean of 17 8 times 1018 n m 1 yr 1 over the past 13 ma if stretching is due mainly to a series of normal faults dipping at about 45 in a seismogenic crust 10 20 km deep the moment magnitude relation from an instrumental magnitude catalogue is log m0 a bm with a 10 970 0 294 b 1 206 in si units this is established from 50 events of magnitude ms 5 3 whose scalar seismic moments m0 have been evaluated in a homogeneous manner for the region by spectral analysis of surface waves at 30 60 s period by contrast published body wave analyses from waveform modelling at 20 s period and moment tensor analyses seem to produce seismic moments which are lower by a factor of two or so on average this moment magnitude relation implies a seismogenic moment release rate due to stretching in the aegean of 14 times 1018 n m 1 yr 1 during the time period 1918 81 and 17 times 1018 n m 1 yr 1 for the period 1964 81 within a factor of two or so uncertainty this implies that the energy release in the brittle crust due to aegean spreading is substantially seismic within the stated accuracy and is also relatively stationary even when compared with the tectonic moment release rates a similar comparison using the same tectonic model shows that the subducting slab is sinking beneath the hellenic arc almost completely aseismically and that processes such as near vertical slab pull and confined thermal expansion could explain most of the observed seismic energy release by internal deformation of the slab the frequency magnitude statistics for the area of active extension has a characteristic earthquake of magnitude 7ms corresponding approximately to fault depths of 10 14 km for an aspect ratio of 2 and a strain drop of 10 4 this is close to the observed seismogenic depth 10 20 km for well determined earthquakes in the aegean area

geochronological framework and tectonic setting of the granitic magmatism in the chaihe moguqi region central great xing an range china abstract we compiled and analyzed 56 u pb zircon ages including 38 ages obtained during the present study and 18 from other sources for granitic rocks of the chaihe moguqi region central great xing an range china magmatism in this area can be divided into eight stages early devonian 399 3 ma late devonian 365 358 ma late carboniferous 322 299 ma early permian 295 282 ma late triassic 231 227 ma early middle jurassic 179 172 ma late jurassic 152 149 ma and early cretaceous 137 120 ma granites were mainly emplaced during the latter four mesozoic stages of magmatism paleozoic granites formed during several stages and were associated with oceanic subduction and the amalgamation of crustal blocks in the eastern fragment of the central asian orogenic belt the late triassic is an important period with respect to the change from the paleo asian ocean tectonic regime to the circum pacific tectonic regime the formation of late triassic granites may have been related to post orogenic lithospheric extension after closure of the paleo asian ocean early middle jurassic granites resulted from either subduction of the paleo pacific plate or subduction during the amalgamation of the jiamusi massif and the songliao terrane whereas the intrusion of late jurassic early cretaceous granites was associated with both the subduction of the paleo pacific plate and the closure of the mongol okhotsk ocean

the late paleozoic to mesozoic evolution of the eastern margin of the central asian orogenic belt in china abstract the north east central asian orogenic belt caob in china records terminal closure of the paleo asian ocean in the mid to late permian along the solonker xar moron changchun suture this marks the end of the overall northward movement of the chinese blocks from a peri gondwana position toward siberia and a switch in tectonic processes to those dominated by activity associated with the paleo pacific plate to the east four distinct changes in tectonic regime can be recognised here in the late paleozoic to early mesozoic i north south compression resulted in orogenesis and gave way to post collisional extension at 260 250 ma with the emplacement of a type granites ii almost coeval with this there was an the onset of east west extension from 250 to 225 ma along the extreme eastern margin of the caob when a seaway opened between the songliao and jiamusi khanka blocks iii the onset of westerly directed compression associated with subduction of the paleo pacific plate from 210 ma resulted in re amalgamation of the jiamusi khanka block with the caob by 190 180 ma and the massive generation of jurassic i type granitoids throughout the region finally iv a change to east west extension from 140 ma onward resulted from roll back of the paleo pacific plate this latter event was accompanied by the emplacement of s type granitoids and the development of sedimentary basins and core complexes it also accompanied a more widespread thinning or delamination of the lithosphere across most of north east china during the cretaceous

timing of destruction of the north china craton abstract the north china craton ncc is the typical example of destruction of an ancient craton however the destruction mechanism and geodynamic controlling factors still remain enigmatic due to controversy on the timing of destruction which is the key to understanding the destruction processes based on temporal and spatial distributions of the igneous rocks and their sources and tectonic settings it is recognized that six stages of tectono magmatism occurred in the ncc during the phanerozoic i e carboniferous to early permian late permian to middle triassic late triassic jurassic early cretaceous and cenozoic among them cenozoic magmatism mainly consists of alkali basalts and is found only occasionally in the eastern ncc the first four stages of magmatism and tectonism related to the southward subduction of the paleo asian plate and the assembly of sino korean and yangtze cratons are locally distributed in limited parts of the ncc reflecting a multiple stage modification of the ncc from the late carboniferous to jurassic however the intensive development of early cretaceous magmatism extensional deformation and associated gold mineralization with significant continental crustal growth indicate that the eastern ncc was destroyed during this time period this destruction was the result of paleo pacific subduction beneath the eastern asian continent with lithospheric removal and or replacement of an ancient cratonic lithosphere by a juvenile oceanic lithosphere

timing and evolution of jurassic cretaceous granitoid magmatisms in the mongol okhotsk belt and adjacent areas ne asia implications for transition from contractional crustal thickening to extensional thinning and geodynamic settings abstract the mongol okhotsk belt and adjacent areas are key areas to study the relationship between the okhotsk and paleo pacific tectonic regimes and their superposition on the older paleo asian regimes during late mesozoic times this paper summarizes the spatial temporal evolution of late mesozoic jurassic cretaceous granitoids and related intrusions in these areas and interprets the magmatic evolution in terms of a transition from contractional crustal thickening to extensional thinning according to 407 published zircon ages these granitoids were mainly emplaced during the intervals 200 180 ma 180 165 ma 165 145 ma 145 135 ma and 135 100 ma jurassic granitoids 200 145 ma predominately occur in the baikal ne mongolia bnem and great xing an range early cretaceous 145 100 ma granitoids are mainly occur in the great xing an range and display a southward younging migration significantly early cretaceous granitoids also extend into the trans baikal area across the mongol okhotsk suture far away from the paleo pacific plate margin in ne china thus they were more plausibly related to post orogenic collapse of the mongol okhotsk orogen from the late jurassic to early cretaceous the granitoids evolved compositionally from calc alkaline and high k calc alkaline i type with some adakite like features to high k calc alkaline and shoshonitic highly fractionated i transitional i a or a type characterized by a significant decrease in their sr y ratios this evolution coincided with a tectonic transition from contractional crustal thickening to extensional thinning combined with regional geology we speculate that the jurassic granitoids were likely derived from melting of the deep seated thickened lower continental crustal lcc sources whereas the cretaceous granitoids produced through crustal melting from an extensional thinning setting our results provide a case study demonstrating that the petrogenesis of granitic magmatism was closely associated with crustal tectonics early jurassic granitoids along the okhotsk belt formed in a subduction collision setting related to closure of the mongol okhotsk ocean whereas late jurassic granitoids in the great xing an range and in the northern north china craton may have formed in a syn or post collisional setting superposed by far field affects of subduction of the paleo pacific plate early cretaceous granitoids in these areas formed in response to post orogenic extensional collapse of the mongol okhotsk belt coupled with back arc extension related to paleo pacific plate subduction

analogue modelling of orthogonal and oblique rifting abstract the three dimensional progressive development of orthogonal and oblique rift systems has been simulated using scaled analogue sandbox models the orientation of the zone of rifting where angle between the rift axis and the extension direction was varied systematically from 90 orthogonal rifting to 75 60 and 45 oblique rifting completed models were impregnated and sectioned both vertically and horizontally orthogonal rift models are characterized by long straight rift border faults and intra rift faults perpendicular to the extension direction oblique rift models are characterized by shorter segmented rift border faults and intrarift faults in the oblique models the rift border faults formed en echelon arrays parallel to the inderlying zone of basement stretching whereas the intra rift faults formed at a high angle to the extension vector increased extension in the moderately oblique and oblique rift systems 60 and 45 caused the intra rift faults to rotate towards parallelism with the rift border faults no strike slip or oblique slip transfer faults were found in any experiments rift border faults and intra rift faults in the models are segmented along strike with relay ramp structures formed between overlapping fault tips along the strike of the rift variations in half graben polarities and offsets of depocentres are accomplished by accommodation zones formed by interlocking conjugate fault arrays the experimental fault patterns compare well with the fault architectures found in those modern or relatively young rift systems where well defined basement controlled strike slip or oblique slip transfer faults are absent an accommodation zone model consisting of interlocking conjugate extension faults is proposed for the along strike switching of half graben asymmetries and offsetting of depocentres in rift systems the fault geometries in the analogue models can be used as templates for recognition of fault styles in both orthogonal and in oblique rift environments

final amalgamation of the central asian orogenic belt in ne china paleo asian ocean closure versus paleo pacific plate subduction a review of the evidence abstract the central asian orogenic belt caob evolved through complex closure of the paleo asian ocean from the neoproterozoic to the late phanerozoic this caused the chinese cratons to collide with eurasia and led to the formation of the world s largest phanerozoic orogenic belt ocean closure commenced in the west and was completed in the east near changchun closure of the paleo asian ocean in ne china was along the solonker xar moron changchun yanji suture and this was likely completed in the late permian although associated activity continued into the triassic there was an overlap in the latest permian early triassic between terminal activity associated with paleo asian ocean closure and the onset of tectonism associated with subduction of the paleo pacific plate this switch in geodynamic setting occurred at 260 250 ma and is reflected by a relaxing of north south directed compression and the onset of east west directed processes related to paleo pacific subduction by the early jurassic events associated with the westward advance of the paleo pacific plate dominated leading to extensive development of i type granites as far inland as the great xing an range from 140 ma the paleo pacific plate retreated eastward resulting in an extensional setting in the early cretaceous the effects of which were enhanced by regional thinning of the lithosphere commonly attributed to delamination throughout this period the eastern asian margin was tectonically complex the north south oriented jiamusi khanka bureya block was rifted away from the eastern margin of the caob in the late triassic but was then re united in the jurassic by westward advancing subduction that affected both the western and eastern margins of the block accretionary complexes continued to evolve in the cretaceous along the whole eastern margin of asia with final accretion of the nadanhada terrane part of the sikhote alin accretionary terrane with the caob at 130 ma followed by the emplacement of s type granites

the enigmatic yinshan fold and thrust belt of northern china new views on its intraplate contractional styles the east to east northeast trending yinshan belt lies within north china extending westward at least 1100 km from china s eastern coast to inner mongolia this intraplate jurassic cretaceous belt underwent contractional and normal faulting folding and contemporaneous terrestrial sedimentation and magmatism current views on its contractional deformational style favor relatively limited thick skinned faulting of archean basement and cover units these views are challenged however by recent discoveries in the eastern part of the belt of south directed ductile nappe formation and large displacement 40 45 km thin skinned northward thrust faulting both involving archean and younger rock units collision of the siberian and north china plates upon closure of a jurassic and early cretaceous mongolo okhotsk ocean more than 800 1100 km to the north may have been responsible for yinshan north south contraction some patterns of contraction e g jurassic cretaceous ductile nappe formation appear to have been influenced by a superposed magmatic regime related to westward subduction of a pacific basin plate beneath the north china plate

formulation of the conceptual model for the tectonic geomorphological evolution of an area five main rivers of greece as a case study abstract this paper associates the tectonic conditions of five rivers integrated drainage networks in northwestern greece for the purpose of formulating the conceptual model of its tectonic and geomorphological evolution the applied methodology consisted in the synthesis of elements from the fields of tectonics and geomorphology using suitable software and gis techniques and the correlation of fault and drainage network trends by the use of rose diagrams to reveal the structures and tectonic events affecting the different orders of the branches and its evolution the relation between morphology tectonics and the development of the drainage network enabled comparison across different areas the grouping of rivers and the identification of areas influenced by the same geodynamic regime in northwestern greece two main groups of rivers were distinguished flowing across areas featuring different tectonic conditions while a transitional zone between them was defined the stages of the area s tectonic and geomorphological evolution were identified with highlighting the definitive impact of tectonic structures on the configuration of the river routes e g the petousi souli fault which forms a natural boundary in the centre of the study area and new elements were added in view of the aforementioned northwestern greece is an independent transitional area in the geodynamic regime of the entire eastern mediterranean notably the methodology applied to these rivers may also be used in other areas thus constituting a standard tool for investigating the geodynamic regime and evolution

structural styles in the deep water fold and thrust belts of the niger delta the deep water niger delta includes two large fold and thrust belts products of contraction caused by gravity driven extension on the shelf that exhibit complex styles of thrusting these contractional structures formed above multiple detachment levels in the overpressured shales of the akata formation using the patterns of growth sedimentation fold shapes fault plane seismic reflections and combined conventional and shear fault bend folding theories we describe and model the structural styles and kinematics of the fault related folds and imbricate thrust systems that compose these belts individual fault related folds involving both forethrusts and backthrusts are characterized by long planar backlimbs that dip less than the associated fault ramps with upward shallowing of dips in growth strata above the backlimbs suggesting components of progressive limb rotation forelimbs are short compared to backlimbs but growth strata show more consistent dips that suggest a component of folding by kink band migration thus we employ a combination of classic and shear fault bend fold theories to describe these structures including the influence of a weak basal detachment zone in the overpressured shales we expand upon these theories to model the kinematics of imbricate thrust systems which display a complex history of thrusting related to spatial and temporal variations in deposition across the delta regional patterns of folded growth strata are used to define break forward break backward and coeval thrusting involving single and multiple detachment levels we define two main types of imbricate thrust systems type i system with a single basal detachment level and type ii imbricate system with multiple basal detachment levels which cause massive structural thickening of the akata formation and refolding of shallow thrust sheets through the sequential restoration of two regional cross sections across these systems we resolve the structural styles the timing and sequences of thrusting as well as the regional amounts of shortening all of which have important implications for hydrocarbon maturation and charge in the deep water niger delta

growth stratal architectures associated to decollement folds and fault propagation folds inferences on fold kinematics abstract in many thrust and fold belts asymmetric folds with overturned or steeply dipping forelimbs and gently dipping backlimbs are commonly interpreted as thrust related folds determining the folding mechanism exclusively from the final fold geometry in the pre growth units is possible only for a limited suite of structures the nature of fold thrust interaction in shallow structures can be inferred by coupling the fold geometric analysis with the study of the syntectonic sediment stratal architectures several factors such as axial surface activity fold uplift limb rotation and limb widening rates together with sedimentation and erosion rates control growth strata patterns because the evolutionary path of most of these parameters depends on the folding kinematics different growth stratal architectures are expected for different thrust related anticlines in this paper we examine the influence of the above factors on growth stratal geometries associated to a simple kink band and then we apply the same approach to kinematic models of decollement folding and fault propagation folding four geometric approaches are used to account for the geometry and kinematics of anticlines located at the tip of a blind thrust fault propagation folding with no excess layer parallel shear fault propagation folding with progressive layer parallel shear constant limb length decollement folding and variable limb length decollement folding whereas fault propagation folding with no excess layer parallel shear is a self similar folding mechanism the other three types involve limb rotation coherent geometries between growth and pre growth sequences develop at high sedimentation rates in the crest of fault propagation folds and incoherent ones in decollement folds minor differences within growth strata patterns occur at low sedimentation rates and when erosion affects the crest of the anticlines

fault superimposition and linkage resulting from stress changes during rifting examples from 3d seismic data phitsanulok basin thailand abstract the phitsanulok basin thailand provides examples of changing fault displacement patterns with time associated with faults of different orientations in the northern phitsanulok basin three main stress states have been identified associated with late oligocene recent fault development 1 late oligocene late miocene approximately e w extension n s shmax main rift stage 2 late miocene pliocene transtension to tranpression e w to ne sw shmax late rift stage and 3 pliocene recent very minor faulting e w extension n s shmax post rift stage syn rift faults tend to strike n s but also follow ne sw and nw se trends and are basement involved the late miocene deformation produced a distinctly different type of fault population from the main rift fault set characterized by numerous small displacement tens of metres faults striking predominantly ne sw most of these faults are convergent conjugate sets aligned in discrete zones and nucleated within the sedimentary basin reactivation of main rift faults trends during the late rift stage favoured strike directions between 350 and 50 the displacement characteristics of three large faults within the basin show variations depending upon fault orientation the low angle 23 30 dip western boundary fault 7 km throw displays little discernible difference in the distribution of displacement on fault zone during the different stress states other than increases and decreases in displacement amount smaller faults exhibit a more selective reactivation history than the western boundary fault and are more informative about fault response to a varying stress field activation of the oblique ne sw striking ntm 1 initially produced a fault divided into three segments splaying into n s trends stress reorientation during the late rift stage finally linked ne sw striking segments the partial linkage of the fault zone at the time of oil migration resulted in the southwestern part of the ntm 1 fault sealing hydrocarbon bearing reservoirs whilst late linkage areas along the northeastern part failed to seal hydrocarbons the n s striking pto 1 fault shows early isolated fault segments linkage during syn rift motion then a more patchy distribution of displacement late in the fault history perhaps due to non optimal orientation of the fault to the regional stress field when compared with the ntm 1 fault the fault characteristics described indicate that where strong pre existing fabrics are present and varying stress regimes have occurred fault population characteristics and evolution of fault displacement can depart considerably from extensional fault populations associated with a single phase of extension

shrimp and electron microprobe chronology of uht metamorphism in the napier complex east antarctica implications for zircon growth at 1 000 c zircons in ultra high temperature uht metamorphosed paragneisses from mt riiser larsen in the napier complex east antarctica were dated by using ion microprobe shrimp and electron microprobe emp both shrimp and emp analyses yield consistent 2520 2460 ma age populations for garnet orthopyroxene bearing paragneiss and leucosomes enclosed within the peak uht event was dated at 2480 ma by shrimp analyses on metamorphic zircons from the garnet orthopyroxene paragneiss and those on magmatic zircons from the leucosomes which are interpreted to be formed at syn uht as obtained by shrimp the uht metamorphic event was terminated no later than 2460 ma minor 2520 ma shrimp age suggests either the onset of prograde metamorphism or another high grade metamorphic event unrelated to the uht emp analyses on metamorphic zircons from sapphirine quartz and osumilite bearing magnesian paragneisses give c 2500 2450 ma ages inherited igneous zircon cores of the magnesian paragneisses yield relatively scattered emp ages ranging over c 3000 2650 ma suggesting that igneous materials of these ages sourced the protoliths of the paragneisses and that they were deposited during the interval c 2650 2520 ma

high resolution passive seismic tomography for 3d velocity poisson s ratio ν and p wave quality qp in the delvina hydrocarbon field southern albania we have studied using traveltimes of p and s waves and initial seismic pulse rise time measurements from natural microearthquakes to derive 3d p wave velocity vp information mostly structural as well as p and s wave velocity vp vs and p wave quality factor qp information mostly lithologic in a known hydrocarbon field in southern albania during a 12 month monitoring period 1860 microearthquakes were located at a 50 station seismic network and were used to obtain the above parameters the data set included earthquakes with magnitudes ranging from 0 1 to 3 0 r richter scale and focal depths typically occurring between 2 and 10 km kohonen neural networks were implemented to facilitate the lithological classification of the passive seismic tomography pst results the obtained results which agreed with data from nearby wells helped delineate the structure of the reservoir two subregions of the investigated area one corresponding to an oil field and one to a gas field were correlated with the

emplacement ages geochemical and sr nd hf isotopic characterization of mesozoic to early cenozoic granitoids of the sikhote alin orogenic belt russian far east crustal growth and regional tectonic evolution abstract the sikhote alin range of the russian far east is an important accretionary orogen of the western pacific orogenic belt in order to study the formation and tectonic evolution of the orogen we performed zircon u pb dating as well as geochemical and sr nd hf isotopic analyses on 24 granitoid samples from various massifs in the primorye and khabarovsk regions the zircon dating revealed that the granitoids were emplaced from 131 to 56 ma cretaceous to paleogene in the primorye region granitoids in the coastal sikhote alin intruded the cretaceous taukha accretionary terrane from ca 90 to 56 ma whereas those along the central sikhote alin fault zone intruded the jurassic samarka accretionary terrane during ca 110 75 ma the oldest monzogranite 131 ma was emplaced in the lermontovka area of the nw primorye region granitoid massifs along the central sikhote alin fault zone in the khabarovsk region formed from 109 to 58 ma thus the most important tectonothermal events in the sikhote alin orogen took place in the cretaceous geochemical analysis indicates that most samples are i type granitoids they have initial 87sr 86sr ratios ranging from 0 7040 to 0 7083 and initial nd isotopic ratios expressed as end t values from 3 0 to 5 0 mostly 0 to 5 the data suggest that the granitoid magmas were generated by partial melting of sources with mixed lithologies including the subducted accretionary complex hidden paleozoic proterozoic basement rocks based on whole rock nd isotopic data we estimated variable proportions 36 77 of juvenile component mantle derived basaltic rocks in the generation of the granitic magmas furthermore zircon hf isotopic data ehf t 0 to 15 indicate that the zircon grains crystallized from melts of mixed sources and that crustal assimilation occurred during magmatic differentiation the quasi continuous magmatism in the sikhote alin orogen suggests that the paleo pacific plate subduction was very active in the late cretaceous the apparently regular progression of granitic intrusion ages from 80 to 56 ma in the taukha terrane may reflect oblique underflow of the paleo pacific plate beneath the eurasian continental margin subduction was not only manifested by granitic intrusion but also by abundant silicic volcanism the late cretaceous paleo pacific plate motion probably changed from parallel or sub parallel to oblique relative to the continental margin of the sikhote alin leading to the change of magmatic source region and geochemical characteristics of the derived igneous rocks late cretaceous rapid sea floor spreading at ca 100 ma induced highly active subduction and led to voluminous magmatism in the entire circum pacific realm finally the present age and isotopic study lends support to the hypothesis of geologic and tectonic correlation between sikhote alin and sw japan

petrogenesis of the linxi granitoids northern inner mongolia of china constraints on basaltic underplating five representative granitoid plutons in the linxi area northern inner mongolia of china divided into two suites are mainly granodiorite and syenogranite and correspond to i and a type granites respectively zircon u pb dating yields an age of 230 ma but most ages range from 149 ma to 111 ma for intrusion of the five plutons suite 1 granitoids show lower sio2 66 1 72 51 and k2o higher al2o3 cao mgo feo and tio2 higher sr ba and eu and lower sm gd nb y and yb than suite 2 granitoids 71 73 78 14 sio2 modeling of major and trace elements shows that fractional crystallization of hornblende and lesser amounts of feldspars for suite 1 and plagioclase and alkali feldspar for suite 2 with overprint of magmatic hydrothermal fluids can explain the geochemical variations the linxi granitoids have initial end t values varying between 5 60 and 2 89 and initial 87 sr 86 sr t ratios ranging from 0 701764 to 0 707654 geochronology of inherited zircons coupled with the nd sr isotopic comparison between granitoids late jurassic basalts and proterozoic gneisses indicates that the linxi granitoids derive from a mixed source of dominantly underplated material or mafic magma with various amounts of the proterozoic gneiss basaltic underplating provides both material and heat to produce the late jurassic to early cretaceous granitoids variation of end t and 87 sr 86 sr t with age suggests involvement in the melting of increasingly greater amounts of the old lower crustal rock our refined equation yields less scattered nd isotope depleted mantle model ages the least fractionated granitoids from each suite have low ca sr rb sr rb ba and k ba ratios and hence represent parental magmas suite 1 parent magma is produced by dehydration melting or derives principally from the fluid metasomatized mantle melting of the underplated tholeiites and their differentiated products generates suite 2 parent magma d 2005 elsevier b v all rights reserved

late jurassic early cretaceous continental convergence and intracontinental orogenesis in east asia a synthesis of the yanshan revolution abstract the basic tectonic framework of continental east asia was produced by a series of nearly contemporaneous orogenic events in the late middle jurassic to early cretaceous commonly the late mesozoic orogenic processes were characterized by continent continent collision large scale thrusting strike slip faulting and intense crustal shortening crustal thickening regional anatexis and metamorphism followed by large scale lithospheric extension rifting and magmatism to better understand the geological processes this paper reviews and synthesizes existing multi disciplinary geologic data related to sedimentation tectonics magmatism metamorphism and geochemistry and proposes a two stage tectono thermal evolutionary history of east asia during the late middle jurassic to early cretaceous ca 170 120 ma in the first stage three orogenic belts along the continental margins were formed coevally at ca 170 135 ma i e the north mongol okhotsk orogen the east paleo pacific coastal orogen and the west bangong nujiang orogen tectonism related to the coastal orogen caused extensive intracontinental folding and thrusting that resulted in a depositional hiatus in the late jurassic as well as crustal anatexis that generated syn kinematic granites adakites and migmatites the lithosphere of the east asian continent was thickened reaching a maximum during the latest jurassic or the earliest cretaceous in the second stage ca 135 120 ma delamination of the thickened lithosphere resulted in a remarkable 120 km lithospheric thinning and the development of mantle derived magmatism mineralization metamorphic core complexes and rift basins the middle jurassic early cretaceous subduction of oceanic plates paleo pacific meso tethys and mongol okhotsk and continent continent collision e g lhasa and qiangtang along the east asian continental margins produced broad coastal and intracontinental orogens these significant tectonic activities marked by widespread intracontinental orogeny and continental reconstruction are commonly termed the yanshan revolution movement in the chinese literature

structural trend analysis by axial surface mapping we present a new method of structural trend analysis in which axial surfaces fold hinges are mapped through grids of seismic reflection profiles and balanced forward models axial surface maps 1 define fold trends lateral terminations and closure in structure 2 constrain underlying fault geometry and slip and 3 highlight and connect regions that can be interpreted by a series of balanced models or cross sections maps of folds in southern california and northeastern pennsylvania are compared with forward model solutions and used to construct balanced three dimensional structural interpretations using fault bend fold theory axial surface maps generated from balanced fault bend fold models define theoretical relationships between map patterns and structural geo etry and fault slip kink band widths between paired axial surfaces in map view are related to underlying fault slip lateral variations in fault slip which can be identified on axial surface maps may cause fold plunge and provide lateral closure lateral changes in subsurface fault geometry which include lateral and oblique ramps are also reflected by terminations bends or offsets of axial surfaces in map view based on these relationships between folding and faulting we develop map view interpretations and balanced cross sections across structures that are consistent with the geology along trend

origin of rollover rollover is the folding of hanging wall fault blocks by bending or collapse in response to slip on nonplanar commonly listric normal faults the shapes of rollover folds are controlled by a number of variables including 1 the shape of the fault 2 the total fault slip after a bed is deposited 3 the direction of relative particle motion in hanging wall collapse 4 the history of sedimentation rate relative to fault slip rate and 5 compaction the importance and role of each of these variables is illustrated by a two dimensional balanced structural modeling technique that treats continuously curved faults as though composed of a large number of straight fault segments in this modeling an active axial surface oriented parallel to the direction of relative p rticle motion in hanging wall collapse emanates from each fault bend and is the instantaneous locus of folding the quantitative correctness of this theory of rollover is tested by modeling natural structures from the gulf of mexico for which both fault shape and fold shape are known from high quality seismic and well sections the direction of hanging wall collapse commonly is in the antithetic or synthetic normal fault or coulomb shear orientations although sliding along weak bedding planes also is an important collapse mechanism in some regions collapse is in the antithetic shear direction for concave fault bends and in the synthetic shear direction for convex bends these collapse directions can be observed directly in some high quality seismic images as axial surfaces emanating from fault bends the shapes of rollovers within growth strata depend strongly on the sedimentation rate relative to fault slip rate as well as the total slip after a bed is deposited the crests of classic gulf coast rollovers are growth axial surfaces along which are abrupt changes in sedimentation rate within the growth st atigraphic interval these changes are produced by deformation of the sediment water interface along active axial surfaces compaction can substantially modify the relationship between fault shape and rollover shape however under certain common conditions the history of compaction can be neglected if the folding is modeled in the compacted state

influence of fault reactivation during multiphase rifting the oseberg area northern north sea rift abstract multiphase rifts tend to produce fault populations that evolve by the formation of new faults and reactivation of earlier faults the resulting fault patterns tend to be complex and difficult to decipher in this work we use seismic reflection data to examine the evolution of a normal fault network in the oseberg fault block in the northern north sea rift system a rift system that experienced permian early triassic and middle jurassic early cretaceous rifting and exhibits n s nw se and ne sw oriented faults both n s and nw se striking faults were established during the permian early triassic rifting as indicated by triassic growth packages in their hanging walls in contrast the ne sw striking faults are younger as they show no evidence of permian early triassic growth and offset several n s and nw se striking faults structural analysis show that a new population of nw se striking faults formed in the lower middle jurassic inter rift period together with reactivation of n s striking permian early triassic faults indicating a ne sw inter rift extension direction during the middle jurassic early cretaceous rifting faults of all orientations n s nw se and ne sw were active however faults initiated during the middle jurassic early cretaceous rifting show mainly n s orientation indicating e w extension during this phase these observations suggest a reorientation of the stress field from e w during the permian early triassic rift phase to ne sw during inter rift fault growth and back to e w during the middle jurassic early cretaceous rift phase in the oseberg area hence the current study demonstrates that rift activity between established rift phases can locally develop faults with new orientations that add to the geometric and kinematic complexity of the final fault population

pattern and kinematic polarity of late mesozoic extension in continental ne asia perspectives from metamorphic core complexes 1 late mesozoic extension in ne asia resulted in the development of a large extensional province metamorphic core complexes mccs are the major features in this province and have 40ar 39ar ages of 130 110 ma for the mylonites and u pb zircon ages of 150 110 ma for the integral granitic intrusions based on this and previous studies this paper summarizes major characteristics of these mccs and recognizes a regional kinematic shear sense most mccs in the transbaikalia region sino mongolia border tract and the northwest central portion of the north china craton ncc show a top to the southeast se shear whereas those in the eastern and southern ncc locally underwent top to the northwest nw shear the three largest basins songliao huabei and ordos in north china are located in the transitional zone between domains of opposing shear sense we interpret the extension in the transbaikalia sino mongolia tract and northwestern part of the ncc to reflect late orogenic collapse of thickened crust following middle late jurassic collision along the okhotsk suture the southeastward extension is probably controlled by crustal scale top to the se tangential shear the transition from contraction to extension is marked by detachment faults that nucleated as extensional crenulation cleavage ecc i e c in sub horizontal ductile shear zones late in orogenic crustal thickening the combined effect of gravitational loading and thermal uplifting is considered to be the origin of the late or post orogenic collapse the top to the nw extension in the ne of the ncc might reflect antithetic sub extensional zones or mesozoic back arc extension as a far field effect of cretaceous pacific plate subduction

parallel thrust and normal faulting in peru and constraints on the state of stress abstract we present evidence for recent normal faulting in the cordillera blanca of peru along planes trending approximately n40 w parallel to the chain this type of faulting suggests that there is an important component of extension perpendicular to the chain and contrasts markedly with the underthrusting of the nazca plate on the west side of peru and with the folding and thrusting observed in the sub andes on the eastern flank of the chain these contrasting styles of deformation and associated stress fields can be explained by buoyancy forces due to the high mountains and crustal roots in so far as this explanation is correct the difference in elevation between zones of normal and thrust faulting can be used to place an upper bound of 500 bars on the average stress difference in the crust

evolution of the mongol okhotsk ocean as constrained by new palaeomagnetic data from the mongol okhotsk suture zone siberia summary this paper presents new data from palaeomagnetic investigations on the upper palaeozoic and mesozoic geological units from the siberian platform and the mongol okhotsk suture zone within the southern portion of the mongol okhotsk suture we collected palaeomagnetic samples from the late permian belektuy formation borzya region 50 7un 116 9ue and the middle late jurassic shadaron formation unda daya 51 5un 117 5ue we sampled the late permian alentuy formation khilok region 50 8un 107 2ue the early to middle jurassic irkutsk sedimentary basin isb 52 0un 104 0ue the late jurassic badin formation mogzon region 51 8un 112 0ue and the early cretaceous gusinoozesk formation gusinoe lake region 51 2un 106 5ue additionally in the northern region of the mongol okhotsk suture apart from the results of the isb and gusinoozersk formations which show very large ellipses of confidence and might be the present day geomagnetic field overprint our results allow us to constrain the evolution of the mongol okhotsk ocean palaeomagnetically from the late permian to the middle late jurassic they confirm that this large permian ocean closed during the jurassic ending up in the late jurassic or the beginning of the cretaceous in the eastern end of the suture zone as suspected on geological grounds however although geological data suggest a middle jurassic closure of the mongol okhotsk ocean in the west trans baikal region our data show evidence of a still large palaeolatitude difference between the amuria and siberia blocks this is interpreted as a result of the quite fast closure of the ocean after the middle jurassic finally our new palaeomagnetic results exhibit very large tectonic rotations around local vertical axes which we interpret as probably arising both from collision processes and from a left lateral shear movement along the suture zone due to the eastward extrusion of mongolia under the effect of the collision of india into asia

growth fault bend folding at southeast lost hills san joaquin valley california synsedimentary deformation has created complex structural and stratigraphic relationships along the west side of the san joaquin valley california this case study of lost hills anticline documents how a simple structural process fault bend folding results in complex growth stratigraphy lost hills anticline is a fault bend fold caused by a step in the lost hills thrust the thrust steps up to the northeast at 27 from a detachment at the base of the tertiary to an upper detachment in the reef ridge formation the lower and upper detachments are at 20 000 ft 6 km and 13 000 ft 4 km displacement on the lower detachment is approximately 4 mi 6 5 km folding consumes 1 2 mi 2 km and the remaining 2 8 mi 4 5 km continues northeast beneath the san joaquin va ley forward and back limb dips of 42 and 27 respectively are consistent with fault bend fold theory pliocene pleistocene sediments onlap a time transgressive unconformity on the northeast front limb but have uniform dip and thickness on the southwest back limb this characteristic growth fault bend fold geometry indicates basinal sediments rolled through an axial surface onto the back limb whereas contemporaneous sediments deposited above the front limb are undeformed basinal sediments onlapping the fold crest indicates fault slip is greater than ramp length onlapping growth sediments indicate folding began during deposition of the etchegoin formation 8 ma and continued to the late pleistocene or holocene corresponding to an average displacement rate on the lost hills thrust of 2 700 ft m y 820 m m y continuous burial of the fold during growth caused each material e physical point in the fold to be at its maximum depth of burial contours of equal density and seismic velocity are relatively flat so that the anticline causes little or no gravity anomaly and less than expected pullup in seismic time sections the geometry of growth sediments imaged on seismic lines indicates lost hills and adjacent anticlines grew by uniform displacement to the northeast with no significant rotation oblique convergence between the pacific and north american plates is manifested as synchronous but spatially separate transcurrent and compressive displacements thus lost hills anticline and perhaps other folds in the area are more appropriately described as compressive folds in a transpressive region than as transpressive folds duplicated lower tertiary strata beneath the lost hills kettleman hills trend are potential targets for petroleum exploration

integrated analysis on gravity and magnetic fields of the hailar basin ne china implications for basement structure and deep tectonics the hailar basin is one of the typical basins among the ne china basin groups which is situated in the east of east asia orogene between the siberia plate and the north china plate based on the detailed analysis of magnetic gravity petrophysical geothermal and seismological data we separate the gravity and magnetic anomalies gma into four orders using wavelet multi scale decomposition wmd the apparent depths of causative sources were then assessed by power spectrum analysis psa of each order low order wavelet detail anomalies were used to study the basin s basement structure such as major faults the basement lithology uplifts and depressions high order ones were used for the inversion of moho and curie discontinuities using the parker method the results show that the moho uplifting area of the hailar basin is located at the ne part of the basin the curie uplifting area is at the nw part and neither of them is consistent with the basin s sedimentary center this indicates that the hailar basin may differ in basin building pattern from other middle and eastern basins of the basin groups and the hailar basin might be of a passive type when the pacific plate was subducting to ne china the frontier of the plate lying on the mantle transition zone didn t pass through the great khingan mountains region so there is not an obvious magma upwelling or lithospheric extension in the hailar basin area finally based on the seismological data and results of wmd a probable 2d crust model is derived from an across basin profile using the 2d forward modeling of the bouguer gravity anomaly the results agree with those from seismic inversion suggesting wmd is suitable for identifying major crustal density interfaces

seismicity and seismotectonics study in southwestern albania using a local dense seismic network abstract the albanides represent a complex orogen made up of a heterogeneous tectonic nappe pile of paleozoic mesozoic and cenozoic domains albania is tectonically active and moderate to strong earthquakes have occurred in the past however abundant microseismicity has not been monitored and studied by a dense seismic network during this study a seismic network of 40 stations was deployed in southern albania for one year a total of 2113 microearthquakes were well located the most accurately located events and 810 focal mechanisms were used in order to define the seismotectonics and the stress pattern in the area results indicate that thrust and strike slip faulting both exist in southwestern albania suggesting a continuation of the complex tectonic setting of the neighboring northwestern greece to the north

tectono sedimentary evolution and hydrocarbon reservoirs in the early cretaceous tanan depression tamtsag basin mongolia abstract the responses of depositional patterns to extensional faulting during the rift cycle are discussed in this article based on an integrated analysis of 3d seismic reflections wire logs and cores from the early cretaceous tanan depression in the tamtsag basin mongolia the synrift succession comprises four third order sequences sq1 4 a four stage fault evolution is defined including early synrift sq1 initial isolate faults early synrift sq2 rapid fault propagation climax synrift sq3 maximum fault relief and late synrift sq4 minor fault activity stages the initial isolated fault stage is defined by separated and small sized half grabens associated with short dispersal alluvium in contrast the rapid fault propagation stage is characterised by much longer dispersal systems of fan delta deposits as rifting progressed a considerable increase in the basin subsidence occurred and the maximum fault displacement led to a dustpan basin geometry the coalescence of depocentres and extensive deep water deposits the observed both sediment starvation and balanced filled patterns in sq3 indicate that caution must be exercised when attempting to correlate reservoirs and source rocks since variations in basin filled patterns would be enhanced by the displacement localisation on several major faults during the significant basin formation during the early period of the climax synrift stage footwall sourced systems were prominent but drainages in prior relay zone sites were mostly decayed or submerged in response to the subsequent degradation of the footwall sources axial sourced braided deltaic systems became more important during the later period an abrupt decrease of faulting at the end of the rift cycle gave a rise to an increased sediment supply and long dispersal axially sourced systems in the tanan depression petroleum exploration shows that fan delta front sandstones in sq2 are the most prospective hydrocarbon reservoirs whereas the nearshore and offshore sub lacustrine fan deposits in sq3 have proved to be secondary potential oil bearing reservoirs this study indicates that sediment dispersal patterns would be significantly re organised by the differential faulting displacement patterns and varied sediment potentials during the different synrift stages the rapid fault propagation allowed the fault arrays to reach their nearly maximum length during the early period of the basin evolution while the displacement remained almost constant this fault growth pattern tends to establish large scale topographic lows including overlapped transfer zones and hanging dip slope hence major drainage catchments and long dispersal depositional systems of sand rich deposits are facilitated during this early fault propagation stage which may be a key aspect for the tectono sedimentary evolution in rift basins in addition the fault and sedimentary relationships defined here may be used as a model when studying less data rich rift basins elsewhere

the ereendavaa range north eastern mongolia an additional argument for mesozoic extension throughout eastern asia mesozoic rift basins locally bounding metamorphic core complexes have been recognized in transbaikalia and northern china numerous basement outcrops located between these two regions in eastern mongolia are considered as pre palaeozoic in age one of these the ereendavaa range appears as a gneissic core marked by amphibolite facies metamorphic conditions the range is overlain to the nw by the unmetamorphosed mesozoic onon basin below the basin the upper part of the range consists of a gently nw dipping shear zone associated with top to the nw motion the structural pattern is consistent with syn extensional exhumation of the range preliminary geochronological data indicate that the shear zone is late jurassic to early cretaceous in age coeval with the onon basin these new data from eastern mongolia constitute a link between transbaikalia and northern china indicating that nw se extensional mesozoic tectonics occurred throughout the entire region

late jurassic early cretaceous closure of the mongol okhotsk ocean demonstrated by new mesozoic palaeomagnetic results from the trans baikal area se siberia summary we present new palaeomagnetic results from the transba ikal area se siberia from the mongol okhotsk suture zone the boundary between the amuria and siberia blocks in order to better constrain the time of closure of the mongol okhotsk ocean in the mesozoic we col lected 532 rock samples at 68 sites in six localities of basalts trachy basalts and andesites from both sides of the mongol okhotsk suture at unda river j 3 51 7 n 117 4 e kremljevka peak k1 51 8 n 117 5 e and torey lakes k 1 50 1 n 115 9 e on the southern side of the suture and at monostoy river j 1 51 1 n 106 8 e ingoda river k 1 51 2 n 112 2 e and bichura town k 1 50 6 n 107 6 e on the northern side progressive thermal demagnetization enabled us to resolve low ltc and high htc temperature components of magnetization at most sites jurassic palaeopoles computed from the htcs show a large discrepancy with respect to the apparent polar wander path of eurasia which we interpret in terms of 1700 2700 km of post late jurassic northward movement of amuria with respect to siberia although ge ological data suggest a middle jurassic closure of the mongol okhotsk ocean in the west trans baikal region our data give evidence of a large remaining palaeolatitude difference between the amuria and siberia blocks in contrast early cretaceous sites cluster remarkably well along a small circle which is centred on the average site location this implies the absence of post early cretaceous northward motion of amuria relative to siberia and demonstrates the pre early cretaceous closure of the mongol okhotsk ocean finally we interpret the very large tectonic rotations about local vertical axes evidenced by the small circle distribution of poles as arising both from collision processes and from left lateral shear movement along the suture zone due to the eastward extrusion of amuria under the effect of the collision of india into asia

petrology and isotopic geochemistry of dawsonite bearing sandstones in hailaer basin northeastern china abstract the co2 gas reservoir sandstones in the hailaer basin contain abundant dawsonite and provide an ideal laboratory to study whether any genetic relationship exists between dawsonite and the modern gas phase of co2 the origins of dawsonite and co2 in these sandstones were studied by petrographic and isotopic analysis according to the paragenetic sequence of the sandstones dawsonite grew later than co2 charging at 110 85 ma the dawsonite 18o value is 7 4 smow and the calculated 18o values of the water present during dawsonite growth are from 11 4 to 9 2 smow this combined with the nahco3 dominated water linked to dawsonite growth suggests meteoric water being responsible for dawsonite growth the 13c values of gas phase co2 and the ratios of 3he 4he of the associated he suggest a mantle magmatic origin of co2 rich natural gas in hailaer basin dawsonite 13c values are 5 3 to 1 5 average 3 4 and the calculated 13c values of co2 gas in isotopic equilibrium with dawsonite are 11 4 to 7 3 these c isotopic values are ambiguous for the dawsonite c source from the geological context the timing of events together with formation water conditions for dawsonite growth dawsonite possibly grew in meteoric derived water atmospherically derived co2 maybe or at least the dominant c source for dawsonite it seems that there are few relationships between dawsonite and the modern gas phase of co2 in the hailaer basin

implications of structural inheritance in oblique rift zones for basin compartmentalization nkhata basin malawi rift ears abstract the cenozoic east african rift system ears is an exceptional example of active continental extension providing opportunities for furthering our understanding of hydrocarbon plays within rifts it is divided into structurally distinct western and eastern branches the western branch comprises deep rift basins separated by transfer zones commonly localised onto pre existing structures offering good regional scale hydrocarbon traps at a basin scale local discrete inherited structures might also play an important role on fault localisation and hydrocarbon distribution here we consider the evolution of the central basin of the malawi rift in particular the influence of pre existing structural fabrics integrating basin scale multichannel 2d and high resolution seismic datasets we constrain the border mlowe nkhata fault system mnf to the west of the basin and smaller mbamba fault mf to the east and document their evolution intra basin structures define a series of horsts which initiated as convergent transfers along the basin axis the horsts are offset along a ne sw striking transfer fault parallel to and along strike of the onshore karoo permo triassic ruhuhu graben discrete pre existing structures probably determined its location and oriented obliquely to the extension orientation it accommodated predominantly strike slip deformation with more slowly accrued dip slip to the north of this transfer fault the overall basin architecture is asymmetric thickening to the west throughout while to the south an initially symmetric graben architecture became increasingly asymmetric in sediment distribution as strain localised onto the western mnf the presence of the axial horst increasingly focussed sediment supply to the west as the transfer fault increased its displacement so this axial supply was interrupted effectively starving the south east while ponding sediments between the western horst margin and the transfer fault this asymmetric bathymetry and partitioned sedimentation continues to the present day overprinting the early basin symmetry and configuration sediments deposited earlier become increasingly dissected and fault juxtapositions changed at a small 10 100 m scale the observed influence of basin scale transfer faults on sediment dispersal and fault compartmentalization due to pre existing structures oblique to the extension orientation is relevant to analogous exploration settings

late mesozoic calc alkaline volcanism of post orogenic extension in the northern da hinggan mountains northeastern china abstract late mesozoic calc alkaline volcanism in the northern da hinggan mountains ndhm ne china exhibits geochemical and sr nd isotopic characteristics similar to those of cenozoic calc alkaline volcanism in the basin and range province usa whole rock k ar dating results show that these volcanic sequences were erupted during 138 116 ma composed of basaltic andesites trachyandesites group 1 hornblende andesites trachytes group 2 and rhyolite lavas group 3 they are characterized by low mgo contents 4 20 lile lree enrichment and significant nb ta depletion as well as a little depleted to slightly enriched nd and weakly enriched sr isotopic ratios group 1 initial 87sr 86sr 0 70502 0 70572 nd t 0 78 to 0 91 group 2 initial 87sr 86sr 0 70497 0 70518 nd t 0 86 to 1 26 group 3 initial 87sr 86sr 0 70510 0 70635 nd t 0 41 to 0 25 the systematic variations in major and trace elements homogeneous sr nd isotope data and temporal consistency among three volcanic groups indicate that they were derived from a similar mantle source metasomatized by fluids related to the closure of the paleo asian and or mongolia okhotsk oceans and were produced through different degrees of fractional crystallization of the primary melts group 1 basaltic rocks were formed through removal of olivine and pyroxene of the primary melts while group 2 trachytes which contain the lowest lree contents e g la 24 28 ppm and relatively less enriched sr and higher nd isotope ratios were generated after removal of a few percent of lree rich minerals such as hornblende clinopyroxene and apatite of melts like group 1 group 3 rhyolite lavas exhibiting the highest abundances of strongly incompatible elements such as rb and k moderate lree contents e g la 28 53 ppm as well as apparently negative eu and sr anomalies represent the final crystallized products following a plagioclase predominant fractionation of melts like group 2 the low mgo contents and evolved affinities of the volcanic rocks imply that beneath the ndhm there existed many crustal magma reservoirs throughout the eruption episodes in which mantle derived primary melts had experienced intense differentiation these facts in combination with the contemporaneous basin and range tectonic regime suggest that the extensive calc alkaline volcanism in the ndhm was attributed to post orogenic diffuse extension rather than either an upwelling mantle plume or mesozoic oceanic plate subduction

a tectonic model for the tertiary evolution of strike slip faults and rift basins in se asia abstract models for the tertiary evolution of se asia fall into two main types a pure escape tectonics model with no proto south china sea and subduction of proto south china sea oceanic crust beneath borneo a related problem is which if any of the main strike slip faults mae ping three pagodas and aliao shan red river asrr cross sundaland to the nw borneo margin to facilitate continental extrusion recent results investigating strike slip faults rift basins and metamorphic core complexes are reviewed and a revised tectonic model for se asia proposed key points of the new model include 1 the asrr shear zone was mainly active in the eocene oligocene in order to link with extension in the south china sea the asrr was less active during the miocene tens of kilometres of sinistral displacement with minor amounts of south china sea spreading centre extension transferred to the asrr shear zone 2 at least three important regions of metamorphic core complex development affected indochina from the oligocene miocene mogok gneiss belt doi inthanon and doi suthep around the asrr shear zone hence paleogene crustal thickening buoyancy driven crustal collapse and lower crustal flow are important elements of the tertiary evolution of indochina 3 subduction of a proto south china sea oceanic crust during the eocene early miocene is necessary to explain the geological evolution of nw borneo and must be built into any model for the region 4 the eocene oligocene collision of ne india with burma activated extrusion tectonics along the three pagodas mae ping ranong and klong marui faults and right lateral motion along the sumatran subduction zone 5 the only strike slip fault link to the nw borneo margin occurred along the trend of the asrr fault system which passes along strike into a right lateral transform system including the baram line

geochronology and geochemistry of middle permian middle triassic intrusive rocks from central eastern jilin province ne china constraints on the tectonic evolution of the eastern segment of the paleo asian ocean abstract to constrain the permian early mesozoic tectonic evolution of the eastern segment of the paleo asian ocean we conducted zircon u pb dating and whole rock geochemical analyses on six middle permian middle triassic intrusive plutons in central eastern jilin province ne china zircons from the six plutons display distinct oscillatory zoning and striped absorption in cathodoluminescence cl images and th u ratios of 0 11 1 41 indicating a magmatic origin zircon u pb dating indicates that the intrusive rocks formed in the middle permian ca 260 ma to middle triassic ca 245 ma in central eastern jilin province the middle permian and middle triassic plutons are composed mainly of strongly deformed monzogranites with affinities to adakitic rocks which are formed from partial melting of thickened mafic lower crust in contrast the late permian the early triassic plutons in central eastern jilin province consist of a bimodal association including gabbros and granitoids and deformed monzonites which typically form in extensional settings these observations along with the results of previous studies on early middle permian granitoids in western jilin province indicate that the eastern segment of the paleo asian ocean underwent the initial closure in central western jilin province during the middle permian and the final closure in eastern jilin province in the middle triassic

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

a short lived but significant mongol okhotsk collisional orogeny in latest jurassic earliest cretaceous abstract the central asian orogenic belt caob is one of the largest orogenic collages on earth which records a long history of accretionary orogenesis from the late proterozoic to the mesozoic although paleomagnetic studies have unanimously suggested that the major mongol okhotsk ocean in the eastern caob closed mainly during the late jurassic early cretaceous few conclusive and self consistent geological studies in central asia and east asia have confirmed the occurrence of this significant collisional orogeny based mainly on basin evolution in the caob tarim block north china block and qaidam qialian block during the late jurassic early cretaceous the present study proposes that a short lived but significant mongol okhotsk collisional event occurred in the latest jurassic earliest cretaceous the rapid closure of the mongol okhotsk ocean was possibly related to the clockwise rotation of siberia which was driven by the continental collision between the siberia craton and the kolyma omolon microcontinent in northeast russia in the late jurassic owing to the clockwise rotation of siberia and the subsequent closure of the mongol okhotsk ocean a number of areas to both the east and the west of the mongol okhotsk suture underwent uplift and erosion including lake baikal transbaikalia sayan ranges altai shan junggar basin turfan basin tarim basin tian shan mohe basin great xing an ranges hailar tamsag basin erlian basin songliao basin east gobi basin yingen basin bei shan yin shan yan shan belt ordos basin chaoshui yabulai basin and northern qaidam basin forming a giant fold and thrust belt in northern china and mongolia the collision probably caused a prominent gap between late jurassic and early cretaceous magmatic episodes in the eastern caob and north china block after lasting for about 10 million years the main portion of the mongol okhotsk ocean closed forming a northeast trending suture during the early cretaceous a remnant ocean still remained in the easternmost part of the mongol okhotsk ocean and the regional compressional setting in east asia related to the closure of the mongol okhotsk ocean changed to escape tectonics driven by the collision of the lhasa block at the southern margin of asia strike slip faulting triggered gravitational collapse of upper crust and delamination of lower crust and mantle lithosphere that was thickened during the mongol okhotsk collision resulting in the development of a continental scale extensional setting in east asia associated with rift basins metamorphic core complexes and igneous rocks

timing of exhumation of the ereendavaa metamorphic core complex north eastern mongolia u pb and 40ar 39ar constraints abstract the occurrence of numerous ne sw trending rift basins that locally bound metamorphic core complexes in transbaikalia northern mongolia and north eastern china indicates that the eastern domain of the central asian orogenic belt was affected by a large scale nw se extensional tectonic event during late jurassic to early cretaceous times available geochronological information about the formation of metamorphic core complexes in the region define partly synchronous periods in transbaikalia 134 121 ma and north china 136 110 ma suggesting dome exhumation during the early cretaceous in north eastern mongolia the ereendavaa range lined by the onon shear zone was recently interpreted as one of these metamorphic core complexes of late jurassic to early cretaceous age on the basis of u pb zircons data from two synkinematic pegmatite dykes however this wide time range remains to be discussed the present work constrains the tectono thermal evolution of the range by providing new mc icp ms u pb zircons ages from pegmatite dykes and metamorphic igneous rocks and mica and amphibole 40 ar 39 ar laser step heating ages from metamorphic and magmatic rocks that crop out within the range the results show that 1 the ereendavaa range was the locus of a widespread magmatic activity prior to its exhumation from late jurassic times 2 cooling of the range began at least at 137 9 0 3 ma as revealed by a 40 ar 39 ar plateau ages obtained from an hornblende sampled within the range core and 3 exhumation along the onon shear zone occurred from 130 3 1 9 ma down to 124 8 0 3 ma as shown by ages of most of micas and amphiboles from the shear zone these more accurate ages are consistent with metamorphic core complex ages from adjacent areas furthermore they argue for an extensional dynamic paroxysm at the scale of eastern asia during a narrow time range in the early cretaceous between ca 130 ma and ca 120 ma

microearthquake seismicity and active tectonics of northwestern greece we carried out a microearthquake survey lasting for six weeks in northwest greece using 18 portable seismograph stations to examine a region in which normal and thrust faulting have been reported in close proximity to one another with this array we located 148 events and determined fault plane solutions for eight events using only rays radiated upwards the seismicity of the region is diffuse with events extending to depths of nearly 30 km and there is a minimum in activity near a depth of 15 km the fault plane solutions exhibit a wide spectrum of fault types and orientations and are not consistent with simple zones of shortening or extension neither tractions applied to the edges or bottom of the region nor deviatoric stresses that compensate for lateral variations in crustal thickness can account for the variety of fault plane solutions we think that the complicated behavior is a manifestation of inhomogeneous deformation due at least in part to a pre existing complicated juxtaposition of structures and formations

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

geochemical characteristics and petrogenesis of adakites in the sikhote alin area russian far east abstract adakitic rocks of the sikhote alin area were emplaced during two main periods the cretaceous 132 98 ma and eocene 46 39 ma these rocks primarily occur in the khanka block and less commonly in the sikhote alin orogenic belt the adakitic rocks record the following chemical compositions sio2 57 74 al2o3 15 18 na2o 3 5 6 1 k2o 0 7 3 2 na2o k2o 1 1 3 9 sr y 33 145 and la yb n 11 53 the hree and hfse in these rocks are remarkably depleted the early cretaceous adakites record end t 1 0 to 3 2 and isr 0 7040 0 7090 and the eocene adakitic rocks record nd t 2 0 to 2 2 and isr 0 7042 0 7058 adakitic features suggest different modes of magma generation a comparison of the sr y and la yb ratios and geochemical data on harker diagrams between the two periods of adakitic rocks reveals differences in their petrogenesis the cretaceous adakites may have been generated by the partial melting of meta basic rocks in a subduction zone accompanied by the emplacement of volcanic arc granitoids therefore the subduction of the paleo pacific plate beneath the sikhote alin was probably initiated during this time the eocene rocks which record increasing adakitic features with increasing silica content are most likely the product of andesite that underwent fractionation of mineral assemblage including clinopyoxene orthopyroxene garnet and amphibole these rocks and associated basalts and rhyolite were formed after cretaceous arc magmatism in the sikhote alin area and were most likely generated by rollback of the subducting pacific plate after the eocene abundant adakitic granitoids of early cretaceous and eocene age occur in the kitakami and abukuma mountains of ne japan consequently it is highly probable that a geological correlation existed between sikhote alin and north japan particularly before the opening of the japan sea

seismicity and associated strain of central greece between 1890 and 1988 summary we examined the seismicity of central greece between 1890 and 1988 using macroseismic and instrumental data to ask two questions 1 does the seismicity of this period reveal all the major tectonic structures that are known to be active and 2 what are the likely strains associated with the seismicity over this period many known active structures have been effectively aseismic for the last hundred years and even the inclusion of all known large events earlier than 1890 reveals no activity associated with the ne coast of evia gulf of argos or graben ne of mt parnassos it is clear that even 100 years data are inadequate for either a reasonable assessment of seismic risk or for a confident estimation of maximum magnitude however we are aware of no earthquakes in central greece during the last 200 yr that were larger than ms 7 0 it is probable that the maximum magnitude is restricted by the maximum length of fault segments which appears to be around 15 20 km the earthquakes of ms 5 8 during 1890 1988 can account for a n s displacement of around 45 70 cm with maximum and minimum estimates a factor of two greater and smaller than this across part of a 1890 1900 triangulation network in central greece that was resurveyed in 1988 the contribution of smaller events may increase this displacement by about 50 per cent this cumulative seismic displacement is similar to that estimated from the geodetic work about 100 cm but a detailed comparison of the two sets of observations will be reported elsewhere a re evaluation of all the important earthquakes of 1890 1988 in central greece is presented in the appendix which summarizes information of use to both earth scientists and engineers

initial constraints on the timing of granitic magmatism in north korea using u pb zircon geochronology abstract the geology of north korea is very poorly known in this paper twenty seven granitic samples from the tumangang belt and the rangnim massif including diorite granodiorite and monzogranite were selected for in situ zircon u pb isotopic dating in the tumangang belt granites formed mainly in the jurassic with one sample giving a triassic age this is contrary to previous views that considered the granites to be permian to triassic in age in the rangnim massif precambrian granitic magmatism mainly took place at 2 1 and 1 9 1 8 ga no archean emplacement ages have been documented in this study although some inherited discordant zircon may be of this age mesozoic magmatism in this area can be divided into three stages with ages of 234 213 173 and 114 109 ma the triassic granites are mostly exposed in the north and the early cretaceous ones in the west the distribution of jurassic granites is less well documented and only one sample was identified in this study however previous data indicate they are more widely distributed in the area the 2 1 and 1 9 1 8 ga precambrian ages are comparable to paleoproterozoic magmatism in northeastern china indicating that the rangnim massif was most likely part of the north china craton during that time however the absence of 2 5 ga granites and the occurrence of 1 2 ga granites indicate that the rangnim massif was probably at the margin of the north china craton and affected by mesoproterozoic magmatism the similarity in age patterns of the mesozoic granites in north korea to surrounding areas of south korea and the liaodong peninsula of northeastern china indicate that they were controlled by subduction of the pacific ocean under eastern asia however roll back or retreat of the subduction zone resulted in a younging trend from northwest to southeast during the cretaceous

geochronology geochemistry and deformation history of late jurassic early cretaceous intrusive rocks in the erguna massif ne china constraints on the late mesozoic tectonic evolution of the mongol okhotsk orogenic belt abstract this paper presents new zircon and sphene u pb ages biotite and hornblende 40 ar 39 ar ages hf isotopic data and geochemical data for five mesozoic plutons in the erguna massif of ne china these data are used to constrain the late mesozoic tectonic evolution of the mongol okhotsk orogenic belt this new dating when combined with previously published ages indicates that the late jurassic early cretaceous j 3 k 1 intrusive rocks can be subdivided into three stages that represent periods of magmatism during the late jurassic 155 ma early early cretaceous 137 ma and late early cretaceous 123 ma in addition the rocks have undergone later deformation recorded by peak ages of 137 and 123 ma the late jurassic and early early cretaceous intrusive rocks in the study area are dominantly syenogranites and are either a type granites or are classified as alkaline series suggesting that they formed in an extensional environment the late early cretaceous intrusive rocks in this area are generally monzogranitic and were emplaced as dikes in an extensional environment along with coeval bimodal volcanics these data combined with the presence of regional unconformities in the northern part of hebei province and western part of liaoning province and the spatial distribution of coeval volcanic rocks in ne china suggest the late jurassic and early early cretaceous magmatisms and the early early cretaceous deformation in this area occurred in an extensional environment related to the delamination of a thickened part of the crust after closure of the mongol okhotsk ocean in comparison the late early cretaceous deformation and magmatism occurred in an extensional environment related to either delamination of the previously thickened crust related to the mongol okhotsk tectonic regime or the subduction of the paleo pacific plate or the combined influence of these two tectonic regimes

sedimentary record and tectonic implications of mesozoic rifting in southeast mongolia the east gobi basin of mongolia is a poorly described late jurassic early cretaceous extensional province that holds great importance for reconstructions of mesozoic tectonics and paleogeography of eastern asia extension is especially well recorded in the structure and stratigraphy of the unegt and zuunbayan subbasins southwest of saynshand mongolia where outcrop and subsurface relationships permit recognition of prerift synrift and postrift mesozoic stratigraphic megasequences within the synrift megasequence three sequences developed in response to climatic and rift related structural controls on sedimentation where best exposed along the northern margin of the unegt subbasin each of the synrift sequences is bounded by unconformities and generally fines upward from basal alluvial and fluvial conglomerate to fluvial and lacustrine sandstone and mudstone resedimented ashes and basalt flows punctuate the synrift megasequence rifting began in the unegt subbasin prior to 155 ma with coarse alluvial filling of local fault depressions subsidence generally outstripped sediment supply and fresh to saline lacustrine environments expanding southward with time dominated the unegt zuunbayan landscape for much of latest jurassic early cretaceous time episodic faulting and volcanism characterized the basin system for the balance of the early cretaceous a brief period of compressional and or transpressional basin inversion occurred at the end of the early cretaceous prior to deposition of a widespread upper cretaceous overlap sequence the driver s of late jurassic early cretaceous extension remain uncertain because southeast mongolia occupied an intraplate position by the beginning of the cretaceous extension in the east gobi basin was coeval with collapse and extension of early mesozoic contractional orogenic belts along the northern and southern borders of mongolia and probably was a linked phenomenon strike slip faulting associated with collisions on the southern asian and mongol okhotsk margins likely also played a role in late mesozoic deformation of the east gobi region perhaps partitioning the gobi from apparently coeval large magnitude contractional deformation in the yinshan yanshan orogenic belt south of the study area in inner mongolia

spatial temporal relationships of mesozoic volcanic rocks in ne china constraints on tectonic overprinting and transformations between multiple tectonic regimes abstract la icp ms zircon u pb ages and geochemical data are presented for the mesozoic volcanic rocks in northeast china with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the paleo asian ocean mongol okhotsk and circum pacific tectonic regimes the new ages together with other available age data from the literature indicate that mesozoic volcanism in ne china can be subdivided into six episodes late triassic 228 201 ma early middle jurassic 190 173 ma middle late jurassic 166 155 ma early early cretaceous 145 138 ma late early cretaceous 133 106 ma and late cretaceous 97 88 ma the late triassic volcanic rocks occur in the lesser xing an zhangguangcai ranges where the volcanic rocks are bimodal and in the eastern heilongjiang jilin provinces where the volcanics are a type rhyolites implying that they formed in an extensional environment after the final closure of the paleo asian ocean the early middle jurassic 190 173 ma volcanic rocks both in the erguna massif and the eastern heilongjiang jilin provinces belong chemically to the calc alkaline series implying an active continental margin setting the volcanics in the erguna massif are related to the subduction of the mongol okhotsk oceanic plate beneath the massif and those in the eastern jilin heilongjiang provinces are related to the subduction of the paleo pacific plate beneath the eurasian continent the coeval bimodal volcanic rocks in the lesser xing an zhangguangcai ranges were probably formed under an extensional environment similar to a backarc setting of double direction subduction volcanic rocks of middle late jurassic 155 166 ma and early early cretaceous 145 138 ma age only occur in the great xing an range and the northern hebei and western liaoning provinces limited to the west of the songliao basin and they belong chemically to high k calc alkaline series and a type rhyolites respectively combined with the regional unconformity and thrust structures in the northern hebei and western liaoning provinces we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the mongol okhotsk suture belt the late early cretaceous volcanic rocks widely distributed in ne china belong chemically to a low to medium k calc alkaline series in the eastern heilongjiang jilin provinces i e the eurasian continental margin and to a bimodal volcanic rock association within both the songliao basin and the great xing an range the volcanics in the eastern heilongjiang jilin provinces formed in an active continental margin setting related to the subduction of the paleo pacific plate beneath the eurasian continent and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust or both late cretaceous volcanics limited to the eastern heilongjiang jilin provinces and the eastern north china craton ncc consist of calc alkaline rocks in the eastern heilongjiang jilin provinces and alkaline basalts in the eastern ncc suggesting that the former originated during subduction of the paleo pacific plate beneath the eurasian continent whereas the latter formed in an extensional environment similar to a backarc setting taking all this into account we conclude that 1 the transformation from the paleo asian ocean regime to the circum pacific tectonic regime happened during the late triassic to early jurassic 2 the effect of the mongol okhotsk suture belt on ne china was mainly in the early jurassic middle late jurassic and early early cretaceous and 3 the late early cretaceous and late cretaceous volcanics can be attributed to the subduction of the paleo pacific plate beneath the eurasian continent

fault related folding a review of kinematic models and their application abstract folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts accretionary wedges fold and thrust belts and intra plate settings in either strike slip compressional or extensional regimes due to their widespread occurrence knowledge about the development of these structures is important to a broad spectrum of geoscience sub disciplines such as structural geology seismology geomorphology petroleum geology and quaternary geology fault related folding has been analyzed intensively over the last 140 years for the sake of this review we divide the folds according to the way the faults and the folds form that is into detachment fault bend and fault propagation folds all fault related folds are caused by changes in fault parameters the simplest method to produce folds is to transport material along faults that have stepped flat ramp flat geometries fault bend fold alternatively the slip can decrease along the length of the fault and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy either a detachment fold or a fault propagation fold is formed respectively detachment folding was first investigated in the early 20th century whereas the full significance of fault propagation folds was recognized quite late in the 1980s seminal work on fault related folding was carried out in the 1930s but quantitative kinematic models have only been available in the last 30 years these models are extremely valuable because they allow a comprehensive understanding of the evolution of fault related folds and lead to more accurate predictions of the sub surface structure from the mid 1990s onwards numerical simulations have been used to identify how fault parameters such as dip and fault bend angle propagation to slip ratio and shape of the trishear zone influence the geometry of the related folding this is directly applicable to the analysis of the shape of anticlines produced however this does not mean that fold geometry is uniquely related to fault geometry on the contrary different kinematic approaches can lead to a similar fold shape

kinematics and timing of continental block deformation from margins to interiors during the deformation of continental blocks the magnitude of tectonic stress generally decreases with increasing distance from the margin of the block however the timing and kinematics of stress transmission from the margins to the interiors of continents are poorly resolved even though this information is critical to our understanding of the dynamics of continental deformation here we present a case study of mesozoic deformation of the north china craton ncc field investigations of mesozoic thrust faults and folds granitic intrusions and dykes combined with zircon shrimp and la icp ms dating and muscovite 40ar 39ar plateau ages reveal the age of the ne sw trending tectonic belts as 180 155 ma where the deformation of the craton margin occurred 10 20 ma earlier than that of the craton s interior although the kinematics of deformation are similar for the interior and the margin of the ncc strain decreases with increasing distance from the margin notably the bulk of the strain in the cratonic interior was focused in zones of pre existing weakness overall we determined that the ncc deformed under conditions of uniaxial compression a conclusion that is compatible with simple rheological models and that the stress magnitude attained in the cratonic interior was much less than that along its margin

control of extensional transfer zones on syntectonic and post tectonic sedimentation implications for hydrocarbon exploration the gulf of suez red sea rift system exhibits superb outcrop examples of extensional transfer zones and displays the control of these zones on syntectonic and post tectonic sedimentation hard and soft linkage transfer zones were identified at variable scales hard linkage transfer zones form inward and outward fault kinks whereas soft linkage transfer zones form relay ramps between overlapping rift parallel faults the two types of transfer zones invariably exerted fundamental control on the deposition of syn and post tectonic sediments flow direction of drainage systems and locations of sediment entry points as well as the intensity of erosion patterns of the structurally high sediment source areas this study highlights the close relationship between the transfer zones and hydrocarbon accumulations in clastic syntectonic reservoirs in rift basins

multibend fault bend folding this paper shows how slightly complex but angular fault shapes with only a few bends lead to broadly curved and or highly complex folds a common perception exists that simple angular fold geometries are a necessary consequence of the normal assumptions of fault bend fold theory namely angular fault bends straight faults and flexural slip to the contrary it is shown here that exact application of these low level assumptions produces great complexity from simple fault shapes this complexity is caused by the combination of 1 generation of new axial surfaces by displacement of hangingwall cut offs past successive fault bends and 2 fragmentation of axial surfaces by mutual interference the result is entwined arrays of fold axial surfaces that produce quasi curved and or complex folds from discrete angular fault bends fold complexity grows in a highly non linear way in the most extreme case the number of fold axial surface segments grows as the fourth power of the number of fault bends this paper presents examples of the immense variety of complex fold geometries that are thus generated 0 1997 elsevier science ltd all rights reserved

phanerozoic granitoids in the central and eastern parts of central asia and their tectonic significance abstract the widespread occurrence of voluminous granitoids is a typical characteristic of the central asian orogenic belt caob in the central and eastern parts of central asia the granitoids occupy a total area more than 8 million km2 with three major area peaks at cambro ordovician carboniferous permian and jurassic six zircon age peaks at ca 500 430 370 330 300 290 260 210 170 and 145 110 ma the early paleozoic granitoids 540 440 ma with age peak at ca 500 ma mainly occur in the northwestern caob and are of calc alkaline i type they probably formed in a subduction setting 500 480 ma within the paleo asian ocean pao and subsequent microcontinental collision ca 460 ma the middle paleozoic granitoids 430 370 ma predominately occur in the nw and southern caob and are characterized by a high k calc alkaline affinity suggesting an accretionary and or a collisional setting the late paleozoic 350 260 ma granitoids are widespread in the caob and formed in variable tectonic settings within an intra continental regime or active continental margins in the pao and in the evolving mongol okhotsk ocean moo carboniferous granitoids 350 300 ma in the northern and northwestern caob exhibit a type alkaline features and formed in a post accretionary settings whereas granitoids in the southern caob show i type calc alkaline features and were generated in an arc setting permian granitoids 290 270 ma are predominantly of i a a type with alkaline signatures associated with coeval mafic magmatism and suggesting a post collisional or intraplate setting contemporaneous with a large igneous province lip in the tarim craton some 270 250 ma calc alkaline granitoids also occur in the southernmost caob combined with 250 245 ma high sr y granitoids these rocks reflect final closure of the pao during 270 250 ma early mesozoic mainly triassic granitoids occur mainly in the eastern caob or eastern central asia the early phase granitoids 250 230 ma are of i and s types whereas the mid and late phase granitoids ca 230 190 ma are of a type and transitional i a type or highly fractionated i type all these granitoids occur in variable settings intraplate post orogenic and continental arc related to three tectonics regimes namely the paleo asian ocean pao the mongol okhotsk ocean moo and the paleo pacific ocean ppo late mesozoic granitoids mainly occur in eastern central asia and were emplaced during 6 major magmatic events at 190 180 180 165 165 145 145 135 135 100 and 100 60 ma the 190 165 ma granitoids are of i type calc alkaline high k calc alkaline and evolved along active margins related to the mongol okhotsk and paleo pacific ocean domains the 145 120 ma granitoids are highly fractionated i transitional i a or a types with high k calc alkaline shoshonitic signatures the magmatic evolution from the late jurassic to early cretaceous coincided with a tectonic transition from contractional thickened crust to extensional thinning the 120 65 ma granitoid magmatism displays a southeastward younging trend suggesting a roll back of the paleo pacific oceanic plate the granitoids in the caob of eastern central asia show variable whole rock nd and hf in zircon isotopic compositions and most have juvenile signatures in some regions e g altai junggar and great xing an the volume of juvenile and slightly juvenile crust

zircon u pb geochronology and petrogenesis of the late paleozoic early mesozoic intrusive rocks in the eastern segment of the northern margin of the north china block abstract zircon u pb dating and whole rock geochemical analysis have been undertaken on late paleozoic early mesozoic intrusive rocks of central jilin province ne china with the aim of constraining the tectonic evolution of the eastern segment of the northern margin of the north china block ncb during the late paleozoic early mesozoic zircon u pb dating indicates that late paleozoic early mesozoic magmatic events can be subdivided into four stages middle permian 270 ma late permian 259 255 ma early triassic 249 ma and late triassic 222 ma the middle permian magmatic event formed peraluminous garnet bearing monzogranites indicative of formation under a compressional tectonic regime related to collision between the ncb and the songnen zhangguangcai range massif the late permian magmatic event formed gabbros and syenogranites a bimodal association that is typical of magmatism within post collisional extensional setting the early triassic magmatic event formed adakitic monzogranites suggesting that they formed from magmas derived from partial melting of a thickened mafic lower crust the late triassic magmatic event formed a series of mafic ultramafic intrusive rocks together with coeval granitoids in adjacent regions and make up a typical bimodal association suggesting that they formed under an extensional environment related to the final amalgamation of the ncb and the songnen zhangguangcai range massif taken together we conclude that the northern margin of the ncb underwent multiple orogenic events between the middle permian and the late triassic with final amalgamation of the ncb and the songnen zhangguangcai range massif occurring in the early triassic an event that led to the final suturing of the solonker xra moron changchun zone

age constraints on late mesozoic lithospheric extension and origin of bimodal volcanic rocks from the hailar basin ne china abstract following the amalgamation of the late mesoproterozoic carboniferous central asian orogenic belt with the siberian and north china cratons ne china underwent late mesozoic lithospheric extension and widespread formation of volcano sedimentary basins we report u pb zircon ages and geochemical data for mafic and felsic volcanic rocks from the hailar basin located about 1000 km north of beijing zircon populations of six felsic rock samples analyzed by laser ablation icp ms yielded similar u pb age spectra ranging from 158 to 125 ma the youngest zircon ages are interpreted as time of magma eruption and the xenocrystic zircon age spectra as evidence for a protracted melting of lower crust due to the underplating of mantle derived magmas during lithospheric extension the volcanic assemblage has a bimodal composition comprising geochemically evolved trachybasalts and felsic volcanic rocks of i and subordinate a type compositions the mafic volcanic rocks have negative nb anomalies high th nb and ce pb ratios low initial e nd values of 0 4 to 3 4 and radiogenic pb and sr isotopes all interpreted as evidence for the melting of passively upwelling asthenosphere and lithospheric mantle previously modified by plate subduction the xenocrystic zircon ages and chemical isotopic data of the felsic rocks support an origin from juvenile crustal protoliths the data of i type felsic rocks are consistent with the melting of underplated mafic protoliths and those of the a type rhyolites support the melting of a crustal source with a composition similar to the i type felsites with apatite controlling their nb anomaly the evidence for the persistent melting of a subduction modified mantle in ne china is in agreement with a model of an extending coupled upper mantle crust system due to a retreating paleo pacific trench

the effect of multiple pre existing weaknesses on formation and evolution of faults in extended sandbox models abstract high resolution three dimensional seismic data show that fault distribution and evolution in rift basins can be very complicated and inconsistent with the classic model of fault formation and propagation fault development in the presence of multiple pre existing weaknesses is still not clearly studied trying to understand the role of multiple pre existing weaknesses in sand models two series of experiments were prepared in the first series of models the mechanical properties of pre existing weaknesses were the same but their orientations were different whereas in the second series of models both mechanical properties and orientations were different the basic characteristics of fault formation and evolution in a rift basin revealed by the models are as follows 1 weakness reactivated faults faults that formed directly along and above the pre existing weaknesses and weakness related faults faults which are not located above the pre existing weaknesses but have similar orientation form much earlier than weakness unrelated faults the order of formation of different weakness reactivated faults is determined by the relative reactivation tendency factors fa of the weaknesses 2 weakness reactivated faults and weakness related faults develop mainly along or parallel to pre existing weaknesses in contrast weakness unrelated faults develop nearly perpendicular to the extension direction 3 a complicated fault system can form during a single extension phase in the presence of multiple pre existing weaknesses and 4 the mode of fault formation and propagation and the increase in length and number of faults have close ties to the nature of pre existing weaknesses fault displacement and length do not have a power law relationship for the majority of faults and there is no unique relationship for different kinds of faults in addition to providing new insights to the formation of complex fault systems the experiment results presented here could be reasonably explained using the reactivation tendency theory they can also be applied to the complicated fault system in rift basin