late cenozoic deformation along the northwestern continuation of the xianshuihe fault system eastern tibetan plateau the xianshuihe fault system is a highly active left lateral slip fault that has played an important role in accommodating late cenozoic crustal deformation of the eastern tibetan plateau the left lateral displacement on the western portion of the fault system the ganzi fault is 80 km based on geologic and geomorphic markers left lateral movement along the fault may have initiated in middle miocene time 12 ma followed by the intensive brittle left lateral movement in late cenozoic time 2 4 ma lying within the headwater regions of the jinsha yangtze river in the yushu region the northwestern end of the xianshuihe fault system consists of four branches these are from north to south the dangjiang fault the yushu fault the batang fault and the xialaxiu fault both the yushu and dangjiang faults display clear geologic and geomorphic evidence for active left lateral slip movement several offset markers of triassic age along the dangjiang fault suggest 39 km of left lateral slip but the geomorphic evidence along the dangjiang and yushu faults suggests only 16 km and 25 km of left lateral slip respectively both the batang and xialaxiu faults demonstrate clear evidence for normal dip slip by an associated series of e w trending grabens and horsts that absorb 9 km of left lateral movement in early to middle pleistocene time about 32 km of left lateral movement on the fault system was estimated to be absorbed by ne sw shortening along the rugged north yushu block in late neogene time this is interpreted to have formed as a rhomb shaped restraining bend along which the left lateral movement along the northwestern end of the fault system was partially transferred into crustal shortening the westward continuation of the dangjiang fault is marked by an e w trending fault which can be traced westward for 150 km to central tibet where it joins the fenghuo shan thrust belt this thrust belt is interpreted to represent the northwestern continuation of the xianshuihe fault system along which 39 km of the left lateral movement was entirely transferred into the n s shortening it indicates that the left lateral movement within the southeastern part of the tibetan plateau along the fault system either caused by lateral extrusion or by clockwise rotation is largely restricted to the northwestern end of the fault system quaternary extension occurred along the northwestern continuation of the xianshuihe xiaojiang fault was coeval with extension along its southern end indicating that the southeastern margin of the plateau underwent clockwise rotation

an insight into crack density saturation rate and porosity model of the 2001 bhuj earthquake in the stable continental region of western india abstract the 2001 bhuj earthquake mw 7 6 source zone is examined in the light of crack density e saturation rate and porosity parameter using new data set derived from a large aftershock sequence recorded by the gujarat seismic network gsnet during november 2006 december 2009 processes of rupture initiations of the mainshock and its aftershock sequence are better understood by synthesizing the dynamic snapshots of the source zone using the new dataset pattern of crustal heterogeneities associated with high e high and high anomalies at depths varying from 20 km to 25 km is similar to those of earlier study by mishra and zhao 2003 the anomalous zone is found extended distinctly by 50 60 km in the lateral direction indicating the reinforcement of cracks and fractured volume of rock matrix due to long aftershock sequence since 2001 bhuj earthquake in the source area it is inferred that the presence of a fluid filled fractured rock matrix with super saturation may have affected the structural and seismogenic strengths of the source zone and is still contributing significantly to the geneses of earthquakes in and around the source zone anomalous pattern of high e with wider distribution of high indicates the existence of micro cracks in the lower crust while high suggests the cementation of cracks through permeation of residual magma metamorphic fluids into the hypocenter zone the results suggest that the existence of residual fluids in the fractured rock matrix in the mid to lower crust might have played a key role in triggering the 2001 mainshock and is still responsible for its continued long aftershock sequences

diffusion closure temperature and age of a mineral with arbitrary extent of diffusion theoretical formulation and applications the commonly used expression of the closure temperature tc of a diffusing species in a mineral as derived by m h dodson contrib mineral petrol 40 1973 259 264 is applicable only to systems which have undergone sufficient diffusion so that even the composition at the center of individual grains is significantly removed from that established at the onset of cooling we have extended dodson s formulation to include cases with arbitrarily small amount of diffusion and applied it to calculate tc and age profiles which would develop in single crystals of different geometries these results permit evaluation of the extent of resetting of mineral age and of ion exchange geothermometers during cooling the measured age profile of a mineral can also be used to constrain its cooling rate these applications have been illustrated for the cases of garnet biotite fe mg exchange geothermometer and the cooling age and closure temperatures of the sm nd and lu hf decay systems in garnet

nd and sr isotopic ratios and trace element geochemistry of epidote from the swiss molasse basin as provenance indicators implications for the reconstruction of the exhumation history of the central alps abstract epidote is a common heavy mineral in sandstones its use as a provenance indicator however is limited because it appears in a wide range of lithologies and geological settings in order to discriminate between mantle and crust derived source rocks we measured isotopic and trace element compositions of detrital epidote from sandstones of the swiss molasse basin the compositions of the detrital epidotes were compared to epidotes from penninic metabasites and austroalpine metagranites from the present day exposures and to epidote from ophiolitic and metagranitic pebbles from the molasse basin we found that nd isotopic ratios of epidote allow a good discrimination between different types of source rocks with end values ranging between 6 1 and 8 6 for metabasic lithologies and between 9 7 and 2 8 for metagranitic lithologies sr isotope ratios reveal similar trends but do not allow such a clear discrimination ba u rb nb and th contents of epidote correlate well with the end values yielding the same provenance signal according to isotopic and trace element compositions three types of epidote bearing sandstones can be distinguished one received epidote from lower austroalpine metagranites another from penninic ophiolites and a third type of sandstone received epidote from both sources the provenance of the detrital epidote has important bearing on the exhumation history of the central alps elucidating the transition between the erosion of lower austroalpine felsic lithologies and the onset of erosion of the penninic lower plate according to our data the penninic lower plate became exposed simultaneously in the hinterland of all molasse fans at 21 20 ma at the same time the relief collapsed as reflected by a drastic decrease of sediment accumulation rates in the foreland basin the combination of both events fits well to the geodynamic scenario of large scale lateral extension processes affecting the central alps in post collisional times

stratigraphy correlation and sedimentary history of adelaidean late proterozoic basins in australia abstract adelaidean late proterozoic time is represented by the precambrian portion of the thick sequence in the adelaide geosyncline its stratotype basin in south australia comparable adelaidean sedimentation including the deposition of glaciogenic sediments is recorded in other intracratonic and epicratonic basins extending northwards across australia in the adelaide geosyncline which lies to the east of the gawler craton and its cratonic platform cover the stuart shelf up to 15 km of mainly shallow water sediments accumulated partly in intracratonic troughs and perhaps partly on a miogeoclinal continental shelf the earliest sedimentation is associated with rifting and basic volcanism with an estimated age of ca 1100 ma it commenced with basal blanket sands shelf carbonates and basaltic volcanics followed by mixed carbonate clastic and evaporitic beds callanna beds the overlying burra group consists of a number of west derived possibly deltaic cycles and magnesite bearing platform carbonates the unconformably overlying late adelaidean umberatana group contains the lower glacial beds including the sturt tillite interglacial siltstone dated at about 750 ma and carbonate and the upper glacial beds the post glacial wilpena group commences with a distinctive cap dolomite above the upper glacials and contains mainly fine to medium clastics and the ediacara metazoan assemblage late adelaidean sedimentation patterns are sufficiently similar in the officer amadeus ngalia and georgina basins of central australia and in the kimberley region western australia to suggest interconnection with the adelaide geosyncline to the south in the amadeus basin the early adelaidean sequence is younger than about 1050 ma but cannot be directly correlated with the early adelaidean formations of the adelaide geosyncline however the late adelaidean glacial and younger sequences are readily correlated they include the lower glacial areyonga formation and the arumbera sandstone i containing elements of the ediacara assemblage in the georgina and ngalia basins mainly late adelaidean sequences including thick glacials can mostly be correlated with the amadeus basin in the kimberley region earliest adelaidean clastics may be represented but only the late adelaidean glaciogenic and associated sediments can be correlated with confidence the tillites commonly overlie glaciated pavements the lower glacials are represented only in a graben while the upper glacials and succeeding sequence are more widespread post glacial shales have been dated at ca 670 640 ma the dominantly carbonate and clastic sequences of the bangemall basin western australia cannot be directly correlated with any type adelaidean but geochronology suggests an earliest adelaidean age ca 1050 ma

provenance of upper precambrian lower cambrian shales in the central iberian zone spain evidence from a chemical and isotopic study geochemical and isotopic sr nd o data are presented for upper precambrian and lower cambrian shale sequences from the central iberian zone spain in order to define geochemical discriminants between them and to assess the nature of the source regions supplying these basins elemental data especially th sc ratios coupled with endt values of 2 5 suggest that the upper precambrian rocks contain a greater proportion of a much younger more mafic component than the lower cambrian sequence which has high th sc and endt of 7 3 coherent trends between elemental and o isotope data imply a homogeneous recycled source as the dominant provenance for the upper precambrian shales whereas a lack of such coherence for the lower cambrian sediments suggests a more heterogeneous provenance the sedimentological geochemical and isotopic data are consistent with the upper precambrian succession being derived ultimately from a polycyclic mixture of young pre cadomian mafic sources and older 2 ga crust in contrast the lower cambrian sequence was mainly derived from old more felsic crust which would have contributed increasingly greater proportions of material as the younger sources were progressively removed by erosion

crustal architecture of central australia based on deep seismic reflection profiling abstract the crustal architecture of central australia is interpreted from deep seismic reflection profiling conducted by the australian geological survey organisation in two surveys in 1985 and 1993 the seismic traverses oriented normal to the main surface structures ran north south in central australia and crossed parts of the arunta block amadeus basin musgrave block and officer basin the present crustal fabric was set in place by the end of the mesoproterozoic by about 1100 ma reactivation of the structures took place in a continental intraplate setting mainly during the middle late palaeozoic alice springs orogeny but also during other orogenic events in the arunta block the crust is dominated by major north dipping planar structures interpreted as thick skinned thrusts many of these thrusts cut deep into the crust and at least one the redbank thrust zone appears to cut and offset the moho in contrast in the northern musgrave block limited field mapping and teleseismic data suggest that the major crustal scale planar structures are south dipping in the central to southern amadeus basin deformation is essentially thin skinned with north directed thrusting confined to the sedimentary succession thus the deep seismic profiles in central australia show a present day crustal architecture that is the response of the crust to mesoproterozoic terrane amalgamation and to later reactivation by intraplate deformational events therefore central australia is a model for intraplate cratonic deformation that occurs in continental crust that is cold thick and strong

seismic signature of the mantle transition zone beneath eastern tibet and sichuan basin abstract the strong interaction between the eastward flow escaping from tibet and the rigid sichuan basin resulted in the rise of the longmenshan however the detailed dynamics in the mantle remains controversial in this study the structure of the mantle transition zone mtz beneath eastern tibet and sichuan basin is investigated using 5080 receiver functions from 51 broadband stations the depth of the 410 km discontinuity is close to the global average except for the longmenshan where the 410 and 660 km discontinuities are found to be depressed by up to 10 25 km and 5 10 km respectively the observed simultaneous depressions of the 410 and 660 km discontinuities distributed along the lms together with proofs from tomography and regional tectonics suggest that asthenospheric flow sinks into the mtz resulting in a high velocity zone as well as variation in the mtz thickness the depressions are not from the traditional clapeyron slopes or temperature variation also the depression of the 410 km discontinuity and the dehydration of wadsleyite are syngenetic both of which originate from the dry mantle flow traveling across the old 410 km interface

the 2019 m w 5 7 changning earthquake sichuan basin china a shallow doublet with different faulting styles the increased seismic activity of the last 10 years in changning county of sichuan province comprised just small mostly ml 5 0 injection induced earthquakes the mw 5 7 earthquake of june 17 2019 is the largest event ever reported there moment tensor of the mainshock was remarkably dominated by a compensated linear vector dipole we resolve its fine structure showing it was a doublet allowing approximation by a thrust and strike slip subevent the mainshock nucleated as thrust faulting which together with the largest aftershocks can be linked with previously known reverse faults favorably oriented to regional stress field contrarily the strike slip segment of the mainshock less favorably oriented was probably facilitated by elevated pore pressure due to previous injections shallow active strike slip faulting not yet mapped in the region is a new feature important for future hazard assessment

nature and tectonic significance of co seismic structures associated with the mw 8 8 maule earthquake central southern chile forearc abstract the mw 8 8 maule earthquake on february 27 2010 affected the central southern chilean forearc of the central andes here we show the results of field investigations of surface deformation associated with this major earthquake observations were carried out within three weeks after the seismic event mostly in the central and northern part of the forearc overlying the rupture zone we provide a detailed field record of co seismic surface deformation and examine its implications on active andean tectonics surface rupture consisted primarily of extensional cracks push up structures fissures with minor lateral displacements and a few but impressive extensional geometries similar to those observed in analogical modeling of rift systems a major group of nw wnw striking fractures representing co seismic extensional deformation is found at all localities these appear to be spatially correlated to long lived basement fault zones the nw striking normal focal mechanism of the mw 6 9 aftershock occurred on march 11 demonstrates that the basement faults were reactivated by the mw 8 8 maule earthquake the co seismic surface ruptures show patterns of distributed deformation similar to those observed in mapped basement involved structures we propose that co seismic reactivation of basement structures play a fundamental role in stress release in the upper plate during large subduction earthquakes the fundamental mechanism that promotes stress relaxation is largely driven by elastic rebound of the upper plate located right above the main rupture zone

push ups fracture patterns and palaeoseismology of the leirubakki fault south iceland abstract field measurements and gps mapping were conducted along the leirubakki fault a 010 trending right lateral strike slip fault located in the holocene lava flows of the south iceland seismic zone because of poor exposures south and north of the holocene lava flow dissected by the fault its length can only be traced for 7 5 km the exposed surface rupture contains fractures that range in size over four orders of a magnitude from the main fault through fault segments 1000 2000 m long fracture arrays 100 250 m long to individual fractures 8 125 m long detailed measurements were made of 63 push ups located at junctions between individual fractures and between fracture arrays and ranging in maximum height from 0 35 to 4 35 m using the push ups the maximum right lateral displacement on the leirubakki fault is estimated at 2 67 m using empirical relationships established globally it is concluded that for a maximum displacement of 2 67 m the true rupture length of the leirubakki fault is around 50 km and that it gave rise to an earthquake of a moment magnitude 7 1

mid neoproterozoic 830 750 ma isotope stratigraphy of australia and global correlation abstract carbon and strontium isotope studies of numerous drillcore and outcrop sections within individual australian neoproterozoic basins in a tectonic and sedimentologic framework have allowed the construction of isotopic records for the interval 830 750 ma this combined with the discovery of a restricted stratigraphic range for the acritarch cerebrosphaera buickii in mid neoproterozoic strata of australia makes possible correlation with successions in canada namibia and spitsbergen that part of the mid neoproterozoic succession in spitsbergen which contains c buickii was previously considered younger than the sturtian glacial epoch but this study has indicated that the akademikerbreen group is older than that a correlation scheme is proposed along five tie lines and is based on a correlation between australia and canada at 830 ma and australia spitsbergen and namibia at 760 ma the lowest ever recorded seawater 87 sr 86 sr ratios in the upper shaler supergroup of canada 0 70561 0 70670 compare with ratios in evaporites of the 830 ma bitter springs formation amadeus basin australia 0 70568 0 70720 comparable 13 c carb records support a correlation at about 760 ma a correlation is made between the heaviest mid neoproterozoic 13 c carb values of 7 2 upper burra group adelaide rift complex and 8 1 kanpa formation western officer basin in australia 8 5 in spitsbergen backlundtoppen formation akademikerbreen group and 8 5 in namibia ombombo subgroup congo craton the stratigraphic range of c buickii in australia and spitsbergen supports this correlation a compilation of 13 c carb and 87 sr 86 sr records between about 830 and 750 ma from australia canada namibia and spitsbergen reveals numerous negative excursions which are not associated with preserved glacial deposits it is necessary therefore to consider additional models to the snowball earth to explain the large and rapid carbon isotopic excursions

a palaeomagnetic study of empress 1a a stratigraphic drillhole in the officer basin evidence for a low latitude position of australia in the neoproterozoic abstract a palaeomagnetic study of the continuously cored empress 1a deep stratigraphic drillhole in the officer basin western australia has revealed a stable high temperature remanence component for the early palaeozoic table hill volcanics and the neoproterozoic lupton steptoe kanpa hussar and browne formations the low inclination of the remanence supports a low latitude position for australia in the neoproterozoic and early palaeozoic these palaeolatitudinal estimates are consistent with the results of previous palaeomagnetic studies of australian neoproterozoic rocks and support a low latitude position during deposition of glaciogenic rocks in the marinoan lupton formation

sequence stratigraphy and depositional controls in late proterozoic early cambrian sediments of amadeus basin central australia the amadeus basin is an isolated intracratonic basin at the center of the australian continent which because of its location and geometry provides an ideal opportunity to investigate depositional controls to this end more than 6 000 km of seismic data in conjunction with a field and well log program have been used in a study of the late proterozoic early cambrian arumbera sandstone the arumbera sandstone was deposited as two major depositional sequences in a shallow marine and deltaic or coastal plain setting similar to that of the devonian catskill delta of north america sediment was supplied from the southwest by heavily laden braided streams during the deposition of the first sequence when sea level was at its maximum sedimentation appears to have been largely aggradational as sediment supply balanced or exceeded basin subsidence the sediments were probably deposited in a coastal or delta plain setting where small scale deltas prograded across the carbonate platform sediments of the julie formation during the accumulation of the second sequence sea level fell rapidly exposing large areas of sediment deposited during the first cycle and restricting edimentation to two steep sided rapidly subsiding subbasins deposition was largely progradational as major deltaic complexes developed on the southern and southwestern margins of the subbasins between the major delta complexes a depositional environment similar to that of the first sequence predominated in the deep subbasins the arumbera sandstone forms a continuous depositional unit across the proterozoic cambrian boundary the unconformable nature of that boundary over much of the earth possibly could be the result of a major eustatic sea level drop the final geometry of the arumbera sandstone and the nature of its sediments were determined largely by local subsidence rates subsidence briefly outstripped sediment supply during a stage of crustal extension as the basin evolved during deposition of sequence 1 depositional space and facies distribution were however fine tuned by salt tectonics and major sea level cycles as at passive margins sequence boundaries appear to be controlled by sea level cycles other variables such as climate the lack of vascular plants and the uplift of the source area were also factors in controlling deposition

ree distribution in the clay fraction of pelites from the southern apennines italy abstract in order to evaluate whether clay minerals or accessory phases control the ree pattern of the only illite is correlated with ree while a smectite rich sample is characterized by the lowest content in ree strong correlations exist between ree and tio2 nb zr and a less significant one with sr no correlations exist between these elements and y r mode factor analysis indicated that three factors account for 87 of the total variance the first factor var 43 2 seems to express mainly the tendency of some resistate minerals to concentrate ree in the fine fraction the second factor var 30 0 may be related to the effect of circulating fluids responsible for dickite genesis the third factor may be linked to the weathering of micaceous phases the ree do not have a significant weight in the second and third factors resistate minerals appear dominant in controlling at least the lree and nb it is proposed that in the studied samples illite likely conveyed ree via the included minerals

teleseismic p wave tomography and mantle dynamics beneath eastern tibet we determined a new 3 d p wave velocity model of the upper mantle beneath eastern tibet using 112 613 high quality arrival time data collected from teleseismic seismograms recorded by a new portable seismic array in yunnan and permanent networks in southwestern china our results provide new insights into the mantle structure and dynamics of eastern tibet high velocity high v anomalies are revealed down to 200 km depth under the sichuan basin and the ordos and alashan blocks low velocity low v anomalies are imaged in the upper mantle under the kunlun qilian and qinling fold zones and the songpan ganzi qiangtang lhasa and chuan dian diamond blocks suggesting that eastward moving low v materials are extruded to eastern china after the obstruction by the sichuan basin and the ordos and alashan blocks furthermore the extent and thickness of these low v anomalies are correlated with the surface topography suggesting that the uplift of eastern tibet could be partially related to these low v materials having a higher temperature and strong positive buoyancy in the mantle transition zone mtz broad high v anomalies are visible from the burma arc northward to the kunlun fault and eastward to the xiaojiang fault and they are connected upward with the wadati benioff seismic zone these results suggest that the subducted indian slab has traveled horizontally for a long distance after it descended into the mtz and return corner flow and deep slab dehydration have contributed to forming the low v anomalies in the big mantle wedge our results shed new light on the dynamics of the eastern tibetan plateau

neodymium isotopic constraints for the origin of mesoproterozoic felsic magmatism gawler craton south australia mesoproterozoic felsic magmatism of the gawler range volcanics and hiltaba suite granites occurred at 1585 1595 ma across much of the gawler craton south australia nd isotopic analysis of this felsic magmatism combined with petrological and geochemical arguments suggest derivation by partial melting of both paleoproterozoic and archean crust the majority of samples analyzed have nd isotopic and geochemical characteristics compatible with the involvement of paleoproterozoic crust stabilized during the 1 85 1 71 ga kimban orogeny as sources for the mesoproterozoic magmatism others require derivation from sources dominated by archean rocks this cycle of paleoproterozoic crustal stabilization followed by involvement of this crust mesoproterozoic felsic magmatism is one previously documented from many parts of mesoproterozoic laurentia on the basis of models proposing east australia antarctica to be the conjugate landmass at the rifted margin of western north america it appears that the voluminous mag

influence of fluids and magma on earthquakes seismological evidence abstract in this paper we present seismological evidence for the influence of fluids and magma on the generation of large earthquakes in the crust and the subducting oceanic slabs under the japan islands the relationship between seismic tomography and large crustal earthquakes m 5 7 8 0 in japan during a period of 116 years from 1885 to 2000 is investigated and it is found that most of the large crustal earthquakes occurred in or around the areas of low seismic velocity the low velocity zones represent weak sections of the seismogenic crust the crustal weakening is closely related to the subduction process in this region along the volcanic front and in back arc areas the crustal weakening is caused by active volcanoes and arc magma resulting from the convective circulation process in the mantle wedge and dehydration reactions in the subducting slab in the forearc region of southwest japan fluids are suggested in the 1995 kobe earthquake source zone which have contributed to the rupture nucleation the fluids originate from the dehydration of the subducting philippine sea slab the recent 2001 geiyo earthquake m 6 8 occurred at 50 km depth within the subducting philippine sea slab and it was also related to the slab dehydration process a detailed 3d velocity structure is determined for the northeast japan forearc region using data from 598 earthquakes that occurred under the pacific ocean with hypocenters well located with sp depth phases the results show that strong lateral heterogeneities exist along the slab boundary which represent asperities and results of slab dehydration and affect the degree and extent of the interplate seismic coupling these results indicate that large earthquakes do not strike anywhere but only anomalous areas which can be detected with geophysical methods the generation of a large earthquake is not a pure mechanical process but is closely related to physical and chemical properties of materials in the crust and upper mantle such as magma fluids etc

3 d seismic structure of the source area of the 1993 latur india earthquake and its implications for rupture nucleations abstract the latur earthquake mw 6 1 of 29 september 1993 is a rare stable continental region scr earthquake that occurred on a previously unknown blind fault in this study we determined detailed three dimensional 3 d p and s wave velocity vp vs and poisson s ratio structures by inverting the first p and s wave high quality arrival time data from 142 aftershocks that were recorded by a network of temporary seismic stations the source zone of the latur earthquake shows strong lateral heterogeneities in vp vs and structures extending in a volume of about 90 90 15 km3 the mainshock occurred within but near the boundary of a low vp high vs and low zone this suggests that the structural asperities at the mainshock hypocenter are associated with a partially fluid saturated fractured rock in a previously unknown source zone with intersecting fault surfaces this might have triggered the 1993 latur mainshock and its aftershock sequence our results are in good agreement with other geophysical studies that suggest high conductivity and high concentration of radiogenic helium gas beneath the source zone of the latur earthquake our study provides an additional evidence for the presence of fluid related anomaly at the hidden source zone of the latur earthquake in the scr and helps us understand the genesis of damaging earthquakes in the scr of the world

riedel shear structures in the co seismic surface rupture zone produced by the 2001 mw 7 8 kunlun earthquake northern tibetan plateau abstract we present a case study of riedel shear structures related to the co seismic surface ruptures produced during the 2001 mw 7 8 kunlun earthquake in northern tibet which are related to strike slip movement along the kunlun fault field investigations and interpretations of high resolution remote sensing images show that the 2001 co seismic surface ruptures striking wnw ese are mainly characterized by riedel shear structures including t fractures and r y and p shears a left lateral shear sense is indicated to assess the riedel shear fabrics quantitatively we measured the azimuth of 19 455 co seismic surface rupture strands the width of rupture zones at 474 profiles and 336 fold axes of mole track structures using 1 m resolution ikonos and 0 61 m resolution quickbird images acquired soon after the earthquake the analytical results show that i the co seismic surface ruptures are generally concentrated in up to five subparallel sub rupture zones with individual sub rupture zones varying in width from 3 to 350 m generally 1 2 km iii t fractures are mainly developed within the alluvial deposits at counterclockwise angles of 15 40 relative to the general trend of the rupture zone iv p shears are also mainly found in the alluvial deposits but at counterclockwise to clockwise angles of 5 10 relative to the general trend and v y and r shears are developed within both the alluvial deposits and basement rocks mainly representing the reactivation of pre existing fault traces the results demonstrate that the co seismic riedel shear structures are primarily controlled by the local geology during surface rupture formation consistent with the idea that riedel shear structures are common fault patterns within strike slip shear zones and that their development is related to the early stages of fault evolution

new constraints on the structure thermochronology and timing of the ailao shan red river shear zone se asia new structural petrographic and 40ar 39ar data constrain the kinematics of the asrr ailao shan red river shear zone in the xuelong shan xls geochronological data reveal triassic early tertiary and oligo miocene thermal events the latter event 33 26 ma corresponds to cooling during left lateral shear in the fansipan fsp range thrusting of the sapa nappe linked to left lateral deformation and cooling of the fsp granite occurred at 35 ma rapid cooling resumed at 25 29 ma as a result of uplift within the transtensive asrr in the daynuiconvoi dncv foliation trends nw se but is deflected near large scale shear planes stretching lineation is nearly horizontal on steep foliations shear criteria indicate left lateral shear sense zones with flatter foliations show compatible shear senses petrographic data indicate decompression from 6 5 kbar during left lateral shear temperatures 700 c 40ar 39ar data imply rapid cooling from above 350 c to below 150 c between 25 and 22 ma without diachronism along strike along the whole asrr cooling histories show two main episodes 1 rapid cooling from peak metamorphism during left lateral shear 2 rapid cooling from greenschist conditions during right lateral reactivation of the asrr in the nw part of the asrr xls diancang shan we link rapid cooling 1 to local denudations in a transpressive environment in the sw part ailao shan and dncv cooling 1 resulted from regional denudation by zipper like tectonics in a transtensive regime the induced cooling diachronism observed in the ailao shan suggests left lateral rates of 4 to 5 cm yr from 27 ma until 17 ma dncv rocks always stayed in a transtensive regime and do not show cooling diachronism the similarities of deformation kinematics along the asrr and in the south china sea confirms the causal link between continental strike slip faulting and marginal basin opening

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

controls on the locus of intraplate deformation in central australia abstract the locus of intraplate deformation in central australia changed from the presently preserved southern margin of the amadeus basin during the late neoproterozoic to early phanerozoic petermann orogeny to the northern margin in the late phanerozoic alice springs orogeny immediately prior to each event the thickness of the amadeus basin sediments varied from as little as 1 5 km in the central parts of the basin to as much as 7 km in the vicinity of the presently preserved margins of the basin with the locus of deformation mimicking the locus of maximum sedimentary thicknesses at the onset of each orogenic event as such these orogenies represent extreme examples of basin inversion a process observed in many intracratonic basins worldwide we show that differential burial of the central australian proterozoic basement complexes beneath the amadeus basin is capable of producing variations in moho temperature of up to 30 c prior to the petermann orogeny and up to 110 c prior to the alice springs orogeny for a brace goetze model of lithospheric rheology the variations in moho temperature equate to variations in effective lithospheric strain rate of 1 4 orders of magnitude implying that variations in thickness of the sedimentary blanket may have played a primary role in localising phanerozoic intraplate deformation in central australia an appealing aspect of this model lies in its corollary that the removal of the sedimentary blanket during denudation of the orogen will be accompanied by dramatic cooling and strengthening of the lithosphere this may provide a plausible explanation for the long term persistence of the extraordinary gravity anomalies 150 mgal developed during these central australian intraplate orogenies

silurian tectonic sedimentary setting and basin evolution in the sichuan area southwest china implications for palaeogeographic reconstructions abstract silurian black shales are among the most significant hydrocarbon source rocks globally and are widespread across the southern and eastern sichuan basin and adjacent areas their tremendous production potential has been demonstrated by the discovery of self sourced shale gas reservoirs in the jiaoshiba field in the fuling area of the sichuan basin in this study we reconstruct the tectonic and palaeogeographic framework of the silurian sichuan basin analyze the distribution of sedimentary facies and subdivide the sedimentary succession into a number of stages understanding the formation and evolution of the silurian basin is necessary to predict its potential for future hydrocarbon exploration and development and may also help to better understand global palaeoceanographic conditions during this interval the sichuan basin in the silurian period was located along the northwestern margin of the yangtze plate which was itself located on the northern margin of gondwana at a low near equatorial latitude the basin was initially composed of an intracratonic depression surrounded by three structural uplifts forming a semi enclosed shallow sea however the basin experienced intraplate tectonic deformation at an early stage followed by continued flexural subsidence and intracratonic deformation preserved silurian strata comprising the longmaxi shiniulan and hanjiadian formations reflect several depositional stages including 1 slow deposition of the basal black shale of the longmaxi formation in a deep water environment due to a transgressive lag following glacial melting in gondwana the resulting sea level rise and intraplate tectonic activity 2 rapid sedimentation during the later stage of longmaxi deposition 3 deposition of the shiniulan formation on a neritic carbonate platform in the southern of the basin 4 deposition of the siliciclastic hanjiadian formation in a deltaic environment

co seismic riedel shear structures produced by the 2010 mw 6 9 yushu earthquake central tibetan plateau china abstract riedel shear structures are often developed within strike slip fault zones this study focuses on the riedel shear structures within the co seismic strike slip surface rupture zone produced by the 2010 mw 6 9 yushu earthquake in the central tibetan plateau china field surveys and structural analysis of the surface ruptures reveal that the co seismic riedel shear structures are characterized by i tension cracks t fractures ii compression structures mainly mole tracks p shears and iii discrete shear faults r and y shears developed in unconsolidated alluvial deposits along the pre existing left lateral strike slip ganzi yushu fault zone the t fractures generally show a right stepping en echelon pattern in contrast the p and r shears indicate a left stepping en echelon pattern the riedel shears are inclined to the general trend of the co seismic surface rupture zone at mean counterclockwise angles of 41 t fractures and 21 r shears and a mean clockwise angle of 35 for the p shears the present results show that i the co seismic riedel shear structures indicate a left lateral strike slip sense for the seismogenic fault and ii the t fractures and p and r shears are the primary riedel shear structures formed during the early stages of the evolution of a strike slip fault constrained by pre existing geologic structures

geochemistry of pelitic and psammopelitic precambrian metasediments from southwestern sri lanka implications for two contrasting source terrains and tectonic settings most of the pelitic and psammopelitic metasediments of southwestern sri lanka are compositionally transitional between shales and greywackes and are of two isotopically distinct types metasediments of the northern part have nd model ages of 1 5 ga and belong to the relatively younger nd model age province of wanni complex wc model ages of two southerly located samples are 2 8 ga being compatible with those of the highland complex hc in accordance with mostly mesoproterozoic to late archaean crustal residence ages cr ni la th and ree data also suggest that the sources of these metasediments are plagioclase fractionated post archaean upper crustal material crustal differentiation of source terrains corresponding to the hc and the wc probably occurred at distinctly different time intervals significant differences exist between the major and trace element chemistry of the metapelites from the wc north and the hc south suggesting derivation from two different source terrains metasediments of the south are slightlymmore siliceous low in sc and v and highly enriched in lree 220 ppm their sources have been chemically evolved felsic igneous rocks and or recycled sediments relatively high v sc feo mgo tio2 and slightly low sio2 in the rocks of the wc indicate contribution of more basic sources cia chemical index of alteration estimates and comparative alkali alkaline earth element patterns suggest relatively fresh source material the o isotope data indicate that the pre metamorphic isotope signatures are preserved and the clay component of the original sediments mainly consisted of illite typifying continental weathering conditions sediments of the south hc were probably deposited in a passive continental margin continental rift environment while those of the northern part wc were probably formed at an andean type active continental margin the two units were tectonically juxtaposed prior to pan african granulite metamorphism

co seismic secondary surface fractures on southeastward extension of the rupture zone of the 2005 kashmir earthquake abstract after the 2005 kashmir earthquake we mapped surface ground fractures in tangdhar uri rajouri and punch sectors and liquefaction features in jammu area lying close to the eastern side of the line of control loc in kashmir india the nw trending ground fractures occurred largely in the hanging wall zone of the southeastern extension of the causative fault in tangdhar and uri sectors the principal compressive stress deduced from the earthquake induced ground fractures is oriented at n10 whereas the causative balakot bagh fault strikes 330 the fault plane solution indicates primarily sw thrusting of the causative fault with a component of strike slip motion the ground fractures reflect pronounced strike slip together with some tensile component the tangdhar area showing left lateral strike slip motion lies on the hanging wall and the uri region showing right lateral strike slip movement is located towards the southeastern extension of the causative fault zone the shear fractures are related to static stress that was responsible for the failure of causative fault the tensile fractures with offsets are attributed to combination of both static and dynamic stresses and the fractures and openings without offsets owe their origin due to dynamic stress in punch rajouri and jammu area which lies on the footwall the fractures and liquefactions were generated by dynamic stress the occurrence of liquefaction features in the out board part of the himalayan range front near jammu is suggestive of stress transfer 230 km southeast of the epicenter the balakot bagh fault bbf the muzaffarabad anticline the rupture zone of causative fault and the zone of aftershocks all are aligned in a 25 km wide belt along the nw se trending regional himalayan strike of kashmir region and lying between the mbt and the riasi thrust murree thrust suggesting a seismogenic zone that may propagate towards the southeast to trigger an earthquake in the eastern part of the kashmir region

geometry of co seismic surface ruptures and tectonic meaning of the 23 october 2011 mw 7 1 van earthquake east anatolian region turkey abstract the 23 october 2011 m w 7 1 usgs 2011a van earthquake was generated by the rupture of a main thrust fault plane striking n60 e and dipping 55 nw with a very small left lateral offset in the western part of the bardakci saray thrust fault zone located in the north of the bitlis zagros suture zone the incompatibly between the subsurface seismologic data and surface deformation data indicates that the fault that generated the earthquake could be blind the main thrust fault plane developed between the northern ercis and southern van continental blocks and indicates that the region is under the influence of a constant nw se pure compressional tectonic regime along with the primary thrust rupture a secondary back thrust fault a left lateral fault with ne strike and a right lateral fault with nw strike occurred in the contraction province additionally the tensional ground cracks that developed on the hanging wall block of the ruptured thrust fault plane due to intra continental collision are either transtensional that mainly fits to left lateral strike slip faulting or extensional deformations on the elevated block

zircon typology combined with smnd whole rock isotope analysis to study brioverian sediments from the armorican massif the identification of source materials contributing to mature terrigenous clastic deposits is made difficult due to a lack of useful discriminant criteria sm nd isotope analysis can provide some indication of the present of mantle derived constituents in clastic rocks however since this method is based on whole rock samples it is only possible to obtain the averaged composition of the different source materials involved moreover sm nd isotope systematics can be strongly influenced by the presence of heavy minerals rich in rare earth elements and or displaying isotopic ratios very different to the sedimentary host in this manner 0 1 of zircon or 0 01 of monazite from an extraneous source is sufficient to modify significatively the sm nd signature of the whole rock the typological study of zircon populations is an extremely valuable tool especially since this mineral is highly resistant and exhibits a morphology controlled by the physical and chemical conditions under which it crystallized zircons that have been reworked in a sedimentary deposit display typologies that make it possible to identify the different igneous rock types present in the source region moreover the typological study can be associated with a single grain pb pb dating this twofold approach was applied to brioverian sedimentary rocks neoproterozoic iii to early palaeozoic in age from the central brittany domain armorican massif nw france it is proposed that these deposits inherited a major component from juvenile crustal materials end 540 1 4 to 6 3 reflecting the presence of igneous precursors with a dominantly mantle derived origin zircon sub types s19 s20 s24 s25 etc to which was added another component of crustal anatectic affinity zircon sub types s2 s6 s7 etc two igneous source regions are identified on the basis of the present study the anatectic granitic massifs of the mancellian batholith 540 ma along with a coeval ignimbritic suite of end proterozoic eocambrian age and the syn and post tectonic dioritic massifs 590 to 530 ma apart from these main sources of clastic supply it is very likely that sporadic contributions arose from basic to intermediate volcanic activity of mantle origin linked to the cadomian orogeny and from the icartian basement

trace elements as source indicators in cratonic sediments a case study from the early proterozoic libby creek group southeastern wyoming to understand how grain size and sorting effect trace element distributions in sediments we compare the compositions of closely associated quartzites pelites and glacial diamictites from the 2 ga libby creek group in se wyoming we found similar ree distributions lree enriched negative eu anomalies and that most compositional differences can be explained by variable quartz dilution trace element distributions from mineral separates in a fuchsite quartzite show that fuchsite contains most of the th u ree sc co and ni and controls the whole rock ree distributions zircon contains most of the zr and hf but 5 of the hree in the pelites and 20 in the quartzites other than zr and hf most trace elements in libby creek sediments are chiefly in micas and were probably in clays in the original sediments increased eu anomalies in upper libby creek sediments signal a sudden increase in eu depleted granitoids in sediment sources which reflects late tectonic uplift mixing models favor granite ba

effects of sedimentary sorting on neodymium isotopes in deep sea turbidites the study of neodymium model ages of sedimentary rocks has added considerably to our understanding of crustal growth and evolution so far however the possible effects of various sedimentary processes on nd isotope distributions have not been fully evaluated here we present nd isotope data for a series of sand mud pairs in modern deep sea turbidites from different tectonic settings which show that sands and muds commonly have significantly different nd isotope compositions that in only some cases are associated with differences in sm nd ratio differences are as great as 7 ndunits corresponding to nd model ages that differ by up to 0 44 gyr and may be explained by separation or unmixing of components from different sources during sedimentary transport and sorting for one sample heavy mineral fraction ation may be indicated these results have implications for studies of nd model ages in sedimentary rocks and for the interpretation of provenance from sedimentary petrography and geochemistry

the crustal and upper mantle structures beneath the northeastern margin of tibet abstract teleseismic receiver functions are used to estimate the crustal thickness v p and v p v s or poisson s ratio beneath the northeastern margin of the tibetan plateau surface wave dispersion measurements are combined with teleseismic receiver functions to improve estimates of model parameters a migration method based on a local velocity model is used to image the upper mantle discontinuities according to the location of pierce points of the direct converted phases on the observed receiver functions we estimate the topography of upper mantle discontinuities the thicker crust in the altyn tagh fault hexi corridor basin may indicate the superposition of crusts during the collision between the indian and the eurasian plates beneath tianshui and its neighboring regions in the eastern margin of tibet high v p and high v p v s values close to uplifts of magma and hot springs might result from the upwelling of mantle materials induced by the collision the depressed 410 km discontinuity might be related to the warm temperature below the northeastern margin of tibet we speculate that the mantle flow beneath the eastern margin of tibet may be turning downward and subsiding into the mantle transition zone

the kinematic evolution of the nepalese himalaya interpreted from nd isotopes neodymium nd isotopes from the himalayan fold thrust belt and its associated foreland basin deposits are useful for distinguishing between himalayan tectonostratigraphic zones and revealing the erosional unroofing history as controlled by the kinematic development of the orogen neodymium isotopic data from the himalayan fold thrust belt in nepal n 35 reveal that the lesser himalayan zone consistently has a more negative nd 0 value than the greater and tibetan himalayan zones our data show the average nd 0 value in the lesser himalayan zone is 21 5 whereas the greater and tibetan himalayan zones have an average nd 0 value of 16 these consistently distinct values throughout nepal enable the use of nd isotopes as a technique for distinguishing between lesser himalayan zone and greater himalayan zone rock the less negative nd 0 values of the greater himalayan rocks support the idea that the greater himalayan zone is not indian basement but rather a terrane that accreted onto india during early paleozoic time neodymium isotopic data from eocene through pliocene foreland basin deposits n 34 show that sediment provenance has been dominated by greater and tibetan himalayan detritus across nepal the nd t values in the synorogenic rocks in western and central nepal generally show an up section shift toward more negative values and record the progressive unroofing of the different tectonostratigraphic zones at 10 ma in khutia khola and 11 ma in surai khola a shift in nd t values from 16 to 18 marks the erosional breaching of a large duplex in the northern part of the lesser himalayan zone this shift is not seen in eastern nepal where the nd t values remain close to 16 throughout miocene time because there has been less erosional unroofing in this region

co seismic mole track structures produced by the 2001 ms 8 1 central kunlun earthquake china extensive co seismic mole track structures have been observed along a 400 km long surface rupture zone associated with the 2001 ms 8 1 central kunlun earthquake north tibet the mole track structures appear in an angular ridge pattern which resembles an angular triangle shaped frame and in a bulge pattern forming small flat hillocks the mole tracks are developed within alluvial fans river channels and bajada and form a linked array of structures along the rupture zone the angular ridge structures resulted from flexural slip folding and faulting of frozen alluvial deposits and surface ice whereas bulge type structures developed by squeezing up of unconsolidated to weakly consolidated alluvial sediments the mole tracks generally formed within the co seismic rupture zone due to contraction in the right bend and right stepover areas between sinistral shear faults and are controlled by the pre existing fault and fold structures along the left lateral strike slip kunlun fault

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

cooling history of the gongga batholith implications for the xianshuihe fault and miocene kinematics of se tibet abstract using thermochronological data and thermokinematic modeling we constrain the timing of late miocene exhumation of the northern portion of the gongga batholith located in southeast tibet along the xianshuihe fault xf we show that rapid exhumation started in the north of the gongga batholith at 9 ma at a rate of 1 85 km myr and slowed down since 4 ma a magmatic pulse occurring during the early pliocene 4 ma has overprinted the rapid miocene exhumation phase in some parts of the batholith which record mainly early pliocene post magmatic cooling slow exhumation since 4 ma is consistent with the present day lower relief observed in the centre of the batholith which contrasts with the rugged high peaks located to the south we propose that the northern segment of the xf the yalahe fault which is not active at present was active between 9 and 4 ma forming a restraining bend that focused exhumation south of it since 4 ma the selaha and the zheduotang faults form the present day restraining bend south of which the highest part of the massif is located including the gongga shan that rises more than 3000 m above the mean elevation of the plateau in the north of the batholith similar peaks have been removed since the miocene by local relief reduction at high elevations considering that the onset of motion along the xf is contemporaneous with the onset of rapid exhumation recorded along the kangding transect at 9 ma and a total offset of 62 km documented for the xf the average slip rate of the xf is 7 mm yr since 9 ma

grain growth in synthetic marbles with added mica and water evolution of grain size in synthetic marbles was traced from compaction of unconsolidated powder through primary recrystallization and normal grain growth to a size stabilized by second phases to form the marbles reagent grade caco3 was mixed with 0 1 and 5 volume mica and heat treated under pressure with added water densification with negligible recrystallization occurred within one hour at 500 c and 500 mpa confining pressure primary recrystallization occurred at 500 550 c causing increases of grain size of factors of 2 5 resulting samples had uniform grain size gently curved grain boundaries and near equilibrium triple junctions they were used subsequently for normal grain growth studies normal grain growth occurred above 550 c at 800 c grain size d increased from 7 m d0 to 65 m in 24 hours growth rates fit the equation d n d 0 n kt where k is a constant and n 2 6 minor amounts of pores or mica particles inhibit normal grain growth and lead to a stabilized grain size dmax which depends on the size of the second phases and the inverse of their volume fraction raised to a power between 0 3 and 1 once dmax is reached normal growth continues only if second phases are mobile or coarsen or if new driving forces are introduced that cause unpinning of boundaries normal grain growth in solnhofen limestone was significantly slower than in pure synthetic marble suggesting that migration is also inhibited by second phases in the limestone

co seismic strike slip fault displacement determined from push up structures the selsund fault case south iceland abstract we analysed push up structures along the selsund fault a n s right lateral strike slip fault activated during the 1912 earthquake in the south iceland seismic zone volume changes and syn tectonic collapse affected push ups during the earthquake followed by post seismic gravitational sagging to determine the push up shortening and hence the strike slip fault motion we define a virtual push up structure without volume change and collapse and we compare it with the present day configuration whereas length comparisons are subject to errors volumetric analysis allows determination of shortening through evaluation of the thickness of the deformed layer affected by the push ups we determine a co seismic peak displacement of 2 4 m along the rupture trace this value is consistent with the magnitude 7 of the earthquake based on empirical relationships neglecting volume changes and collapse effects gives underestimated displacement the new method for analysing push up structures thus allows better determination of magnitudes of ancient earthquakes along strike slip faults

mid neoproterozoic biostratigraphy and isotope stratigraphy in australia abstract palynomorph and stromatolite assemblages from mid neoproterozoic strata of australia appear highly significant when collated with results obtained from isotope stratigraphy and allow correlation across the centralian superbasin and adelaide rift complex the majority of palynomorphs from the lower mid neoproterozoic 830 ma have limited biostratigraphic value although a few apparently have restricted ranges carbonates at this stratigraphic level contain the distinctive stromatolite acaciella australica and other taxa of the acaciella australica stromatolite assemblage these carbonates have 13ccarb values of between 4 and 0 and associated anhydrite has 87sr 86sr ratios of 0 7069 these depleted 13ccarb values are immediately preceded by values of 6 1 in the western officer and amadeus basins of the centralian superbasin similar c and sr isotopic features are seen in the similarly aged upper shaler supergroup of canada upper mid neoproterozoic 760 ma carbonates contain the distinctive stromatolite baicalia burra and other stromatolites of the baicalia burra stromatolite assemblage siliciclastic horizons in the same interval contain the acritarch cerebrosphaera buickii and have 13ccarb values of between 0 and 8 the highest mid neoproterozoic 13ccarb values of between 6 7 and 8 1 occur within the stratigraphic range of c buickii in australia in the western officer basin and adelaide rift complex the mid neoproterozoic 13ccarb peaks are preceded by values of ca 0 the apparently restricted range of c buickii in australia suggests the need for reinterpretation of the stratigraphic position of its occurrence in the svanbergfjellet formation akademikerbreen group spitsbergen which was previously considered a post sturtian glacial deposit

surface deformation and tectonic background of the 2019 ms 6 0 changning earthquake sichuan basin sw china abstract the june 17 2019 ms 6 0 changning earthquake at a depth of 3 5 km struck the changning anticline fold system no active faults have been observed in the region some studies have attributed the earthquake to the regional shale gas exploitation following the earthquake we conducted a field survey to investigate co seismic surface deformation in the area and observed many surface fractures and uplifted areas our work indicated that the deformation followed a riedel shear pattern the fractures and uplifted areas represent t fractures and s extrusions respectively the observed riedel shear pattern is indicative of left lateral strike slip motion to ascertain the relationship between the riedel shear pattern and regional tectonics we investigated the trends in layer striations and fault scratches the results indicated that there were two stages in the evolution of the anticline in the first stage the principal compressive stress that dominated the original formation of the anticline trended ne sw in the second stage the regional principal compressive stress shifted to the current e w trend generating oblique motion that included reverse and left lateral components we propose that the tectonic stress field in this region had a strong bearing on the focal mechanism of the mainshock and the co seismic surface deformation both the eastward expansion of the xianshuihe area and southeastward expansion of the longmen shan have affected the current changning anticline fold system

the 2005 qeshm island earthquake iran a link between buried reverse faulting and surface folding in the zagros simply folded belt summary the 2005 november 27 qeshm island earthquake m w 6 0 provides an excellent opportunity to study coseismic deformation in the zagros simply folded belt with synthetic aperture radar interferometry insar typical of reverse faulting in the zagros slip in the qeshm island earthquake did not rupture the surface however ascending and descending track interferograms spanning the earthquake both show an elliptical pattern of surface deformation in the central part of the island we invert the interferometric data to attain a set of source parameters these show 1 m slip on a steep 50 north dipping reverse fault extending from a maximum depth of 8u p to 4 km below the surface limited aeromagnetic data suggests the fault ruptured the sedimentary cover whether its deepest parts also affected the crystalline basement is not clear source parameters from seismic body wave modelling agree with those from the interferometric modelling using the insar derived model we produce a map of coseismic vertical displacements with which we compare the surface structure of the island coseismic uplift is centred on the eastern end of a major anticline which trends e w parallel with the fault the long term growth of this fold may be controlled primarily by repeated earthquakes on this fault however the uplifted region extends to parts of other nearby folds whose long term growth must have other controls moreover a region of coseismic subsidence lies very close to a part of the qeshm island coastline that displays raised beaches evidence of quaternary uplift therefore the link between reverse faulting and surface folding is not wholly evident from this earthquake alone the local structure is complicated by orthogonal fold axes it may take a large earthquake in a simpler structural setting within the zagros to establish convincingly whether a one to one correlation between faulting and folding exists

intraplate deformation in central australia the link between subsidence and fault reactivation abstract central australia has experienced two intraplate orogenic events involving significant north south shortening the late neoproterozoic to early cambrian petermann orogeny and the devonian to carboniferous alice springs orogeny in each event pre existing structures inherited from mesoproterozoic terrain amalgamation were reactivated and basement rocks exhumed from beneath thick sedimentary successions accumulated in the centralian superbasin the pattern of fault reactivation during these events shows a striking similarity to the pattern of subsidence in the overlying basin immediately prior to the petermann orogeny the centralian superbasin was thickest in the vicinity of the musgrave block the region in which deformation was subsequently localised at the same time crustal scale faults elsewhere in central australia that were covered by a relatively thin sheet of sediment remained inactive despite being favourably oriented to accommodate the north south shortening between the petermann and alice springs orogenies subsidence patterns shifted such that fault systems in the arunta block and also those in the southern musgrave block were buried by significant thicknesses of sediment whereas the major structures that were exhumed during the petermann orogeny were not significantly buried during the alice springs orogeny reactivation once again occurred along the most deeply buried faults even in the instances where those faults had remained inactive during the earlier petermann orogeny importantly the major petermann aged structures that were not buried during renewed subsidence remained inactive during the alice springs orogeny the record of reactivation implies that the presence of pre existing crustal scale faults alone was insufficient to localise deformation rather fault reactivation appears to have required a priming process that modulated the strength of the lithosphere on a regional scale the correspondence between the distribution of basement fault reactivation and subsidence patterns during both the petermann and alice springs orogenies implies a link between relatively thick sedimentation and long term lithospheric weakening we show that this link is compatible with the thermal effects of a thick sedimentary blanket in the context of central australia the mechanical impact of basin formation is likely to be enhanced by the presence of regionally elevated heat production in the proterozoic basement

sm nd isotopic evidence for the provenance of sediments from the adelaide fold belt and southeastern australia with implications for episodic crustal addition abstract in south australia late proterozoic and cambrian sediments were deposited in basins formed within archaean to early mid proterozoic basement these sequences were subsequently deformed and uplifted by the cambro ordovician delamerian orogeny to form the adelaide fold belt in using the adelaide fold belt to address models for lithospheric evolution it is necessary to understand the mechanisms of basin formation and whether the sequences merely reflect reworking of existing cratonic material or if there were new crustal additions this study presents geochemical and isotopic data on the sediments and basement rocks to complement existing data on the delamerian igneous rocks as a means of investigating these questions the data reveal that the archaean mid proterozoic basement rocks of the gawler craton have nd depleted mantle model ages which average about 2 6 ga and nd values at 800 ma in the range 9 to 24 or at 500 ma from 11 to 28 the late proterozoic adelaidean sediments however have an average model age of 1 9 ga and initial nd values in the range 5 to 11 the sequence can be divided into lowermost rift phase sediments derived from erosion of local gawler craton material and a subsequent widely distributed thermal sag phase sedimentation whose isotopic signature is not compatible with the basement this implies that a more primitive or juvenile source was accessed via broadening of the provenance region the cambrian sediments have slightly older model ages 2 1 ga and lower nd 9 to 13 and can be interpreted as mixtures of basement and reworked adelaidean detritus the early palaeozoic sedimentary sequences of the lachlan fold belt to the east have isotopic compositions very like the south australian late proterozoic and cambrian sequences they have an average model age of 1 85 ma but much higher k 2 o na 2 o this indicates that the widespread flysch of eastern australia is the result of recycling of the late proterozoic and cambrian sediments by erosion of the adelaide fold belt with some modification by the mixture of the cambro ordovician mafic and felsic magmatic rocks in this orogen our data suggest regional intracontinental crustal evolution combined with recycling of older crustal material with new additions from the mantle during orogenesis and to a lesser extent episodes of extension and sedimentation

is there a big mantle wedge under eastern tibet abstract the big mantle wedge bmw model was originally proposed to explain the origin of the intraplate changbaishan volcano in ne china where the subducting pacific slab becomes stagnant in the lower part of the mantle transition zone mtz the bmw is defined as a broad region in the upper mantle and upper part of the mtz overlying the long stagnant pacific slab under eastern tibet prominent low velocity low v anomalies are revealed in the upper mantle whereas an obvious and broad high velocity high v anomaly is imaged in the mtz from the burma arc northward to the kunlunshan fault zone and eastward to the xiaojiang fault zone in addition receiver function analyses clearly illustrate a thickened mtz in a similar area hence we conclude that there is a bmw structure under eastern tibet which can explain the deep origin of the tengchong volcano and generation of large crustal earthquakes in the region the tengchong volcano is caused by hot and wet mantle upwelling in the bmw and fluids from dehydration reactions of the stagnant indian slab in the mtz the 2008 wenchuan earthquake ms 8 0 took place in a transitional belt from the low v songpan ganzi block to the high v sichuan basin suggesting that the occurrence of the wenchuan earthquake was affected by the bmw structure these results shed new light on the mantle structure and dynamics under eastern tibet

regional high pressure metamorphism during intracratonic deformation the petermann orogeny central australia the petermann orogeny is a late neoproterozoic to cambrian c 560 520 ma intracratonic event that affected the musgrave block and south western amadeus basin in central australia in the mann ranges within the central musgrave block mesoproterozoic granulite facies gneisses granites and mafic dykes have been substantially reworked by deep crustal non coaxial strain of late neoproterozoic to early cambrian age dolerite dykes have recrystallized to garnet granulite facies assemblages associated with the development of a mylonitic fabric at p 12 13 kbar and t 700 750 c migmatization is restricted to discrete shear zones which represent conduits for hydrous fluids during metamorphism peak metamorphism was followed by decompression to c 7 kbar reflecting exhumation of the terrane along the south dipping woodroffe thrust in scattered outcrops north of the mann ranges peak metamorphism occurred at p 9 10 kbar and t c 700 c the woodroffe thrust separates these deep crustal mylonites from granites that were metamorphosed during the petermann orogeny at p c 6 7 kbar and t c 650 c the similarity in peak temperatures at different crustal levels implies an unusual thermal regime during this event the existence of a relatively elevated geotherm corresponding with th and k enriched granites that were in the mid crust during the petermann orogeny suggests that radiogenic heat production may have substantially contributed to the thermal regime during metamorphism this potentially has implications for the mechanisms by which intra plate strain was localized during this event

geology and geochemistry of arenite quartzwacke from the late archaean sandur schist belt implications for provenance and accretion processes abstract detailed geological petrological and geochemical studies have been carried out on an arenite quartzwacke suite of rocks constituting a part of the late archaean sandur schist belt in dharwar craton southern india for understanding the nature of provenance for these sedimentary rocks the arenite quartzwacke consists of rounded to sub rounded and angular fragments of monocrystalline polycrystalline quartz quartzite and chert embedded in a fine grained matrix of quartz and sericite while arenites are more siliceous sio 2 80 92 wt the quartzwacke have relatively lower silica content ca 69 78 wt the arenites and quartzwackes have cia values ranging from 76 to 96 which suggest intense chemical weathering this is further corroborated by the positive correlation between al 2 o 3 and tio 2 in both these rock types the a cn k modeling of arenites and quartzwackes show evidence for addition of k 2 o during later metasomatic alteration in the a cnk fm ternary diagram all the samples plot along a mixing line between chlorite and sericite indicating alteration during k metasomatism and the presence of mafic rocks in the source the high concentration of hfse such as zr hf nb and ta and the trace element ratios th sc la sc th u and ce th in the arenite quartzwacke indicate a mixed provenance the rare earth element modeling of quartzwackes considering tonalite granite and amphibolite end members in the provenance suggests equal proportions of mafic and felsic end members a composition comprising of 25 tonalite 25 granite 50 amphibolite in the provenance appears to match with the observed range of ree patterns of quartzwackes the presence of higher proportions of granite in the provenance is evidenced by the large negative eu anomalies in these sediments field evidence and structural discordance suggest that the arenite quartzwacke suite is an allochthonous part of the sandur schist belt

crustal heterogeneity in bulk velocity beneath the 2001 bhuj earthquake source zone and its implications in order to resolve an enigmatic issue relating to the existence of fluid related or temperature related anomalies at the mainshock hypocenter of the 2001 bhuj india earthquake m w 7 6 an estimate of the 3d bulk sound velocity structure is made from the inverted high quality p and s arrival times from a total of 368 aftershocks recorded by 12 temporary seismic stations installed following the 2001 bhuj earthquake results reveal strong lateral and vertical heterogeneity in bulk velocity graphic 1 beneath the source zone the 2001 bhuj mainshock and its aftershock source zones are associated with anomalously high bulk sound velocity high graphic 2 indicating high bulk elastic strength of the source rocks at the mainshock hypocenter due to high pore pressures of the fully saturated cracked rocks associated with solute precipitation through the processes of acoustic fluidization and cementation the interpretation of bulk velocity tomograms suggests that the processes of mineral dehydration and permeation of sea surface water through several active quaternary faults down to the deep crust might have contributed to in situ fluid related material heterogeneity in bulk velocity within the fluid filled fractured rock matrix in the paleorift zone at the 2001 bhuj mainshock hypocenter which in turn increased pore pressure lowered the effective stress and brought the system into a brittle failure high graphic 3 in the intersecting fault geometry in the fractured rock matrix at the mainshock hypocenter can be taken as evidence for the strong role of fluids in association with the intraplate earthquake of the indian peninsula 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif

structure and deformational character of strike slip fault zones strike slip fault zones observed either in the field or in model experiments generally consist of several subparallel faults which make these zones complicated in geometry and kinematics the geometry of a strike slip fault or shear zone is dependent on arrangement pinnate or en echelon on step left step or right step and on the rank smaller faults within larger faults of the subparallel fault the relations and interactions of these three factors create a variety of dynamic circumstances and tectonic settings within the strike slip fault zones these include pull aparts in the release area between subparallel faults push ups in the jogs where the subparallel faults overlap and pivotal movements or rotation of single faults along the whole fault zone each kind of tectonic setting is in itself characteristic each setting consists of many subtypes which are controlled chiefly by the geometric parameters of the subparallel faults one of the most important phenomena revealed in the field work is two different kinds of evolution of strike slip fault zones one is the evolution of a zone with a tensile component which is related to the growth of rock bridges and the other of one with a compressional component which develops by the destruction of rock bridges in this paper we discuss on the basis of recent research on four strike slip fault zones in china the essential characteristics of strike slip faults and the possible causes of the observed structural phenomena attention is focussed on the deformation development and distribution of horizontal displacements within strike slip fault zones

clastic metasediments of the early proterozoic broken hill group new south wales australia geochemistry provenance and metallogenic significance whole rock analyses of samples of pelite psammite and psammopelite from the early proterozoic broken hill group willyama supergroup in the broken hill block new south wales australia reveal distinctive geochemical signatures major element data show high al2o3 and k2o low mgo and na2o and relatively high fe2o3tmgo ratios compared to average early proterozoic clastic metasediments high field strength elements hfse are especially abundant including nb most 15 27 ppm ta most 1 0 2 2 ppm th 17 36 ppm hf 4 15 ppm and zr most 170 400 ppm y 33 74 ppm is also high concentrations of ferromagnesian elements are generally low sc 20 ppm ni 62 ppm co 26 ppm cr most 100 ppm data for rare earth elements rees show high abundances of light rees lacn 116 250 chondrite lacn 437 in one sample high lacnybcn ratios 5 6 13 9 and large negative eu anomalies eueu 0 32 0 57 the geochemical data indicate derivation of the metasedimentary rocks of the broken hill group by the erosion mainly of felsic igneous or meta igneous rocks high concentrations of hfse y and rees in the metasediments suggest a provenance dominanted by anorogenic granites and or rhyolites including those with a type chemistry likely sources of the metasediments were the rhyolitic to rhyodacitic protoliths of local quartz feldspar biotite garnet gneisses e g potosi type gneiss that occur within the lower part of the willyama supergroup or chemically similar basement rocks in the region alternative sources may have included early proterozoic anorogenic granites and or rhyolites in the mount isa and or pine creek blocks of northern australia or in the gawler craton of south australia metallogenic considerations suggest that the metasediments of the broken hill block formed enriched source rocks during the generation of pegmatite hosted deposits and concentrations of la ce nb ta th and sn in the region li be b w and u in pegmatite minerals of the district may have been acquired during granulite facies metamorphism of the local metasediments

outward growth of the tibetan plateau during the cenozoic a review abstract the surface uplift history of the tibetan plateau tp offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the asian monsoon various models have been proposed to reveal the surface uplift history of the tp but controversies remain we evaluate these models using data from sedimentology and stratigraphy structural geology magmatism exhumation and paleoaltimetry studies structural analyses indicate that thrust belts which spread from the central tp outward toward its surrounding margins accommodated most of the india asia convergence and facilitated crustal shortening and thickening in the central tp eocene adakitic rocks located in the qiangtang and the lhasa blocks likely were generated by partial melting of an eclogitic source paleogene 50 30 ma potassic rocks only occur in the qiangtang block whereas late oligocene late miocene 26 8 ma potassic rocks occur both in the qiangtang and lhasa blocks low temperature thermochronologic ages in the central tp are older than 40 35 ma whereas those in the margins are younger than 20 ma mostly late miocene and pliocene pleistocene in age independent paleoaltimetry estimates suggest that the lhasa and qiangtang terranes attained their current elevations during the eocene most likely due to the initial collision between india and lhasa whereas the hoh xil basin area to the north and himalayas to the south were still low even below sea level in the latter case we argue for an inside out growth pattern for the tibetan plateau the tp grew southward and northward from a nucleus of high topography and is likely to continue expanding along the mazar tagh fault to the northwest the kuantai shan hei shan longshou shan to the northeast the longquan shan to the east and the shillong plateau to the south if the northward force of india would not diminished

tomography of the source area of the 1995 kobe earthquake evidence for fluids at the hypocenter seismic tomography revealed a low seismic velocity 5 and high poisson s ratio 6 anomaly covering about 300 square kilometers at the hypocenter of the 17 january 1995 magnitude 7 2 kobe earthquake in japan this anomaly may be due to an overpressurized fluid filled fractured rock matrix that contributed to the initiation of the kobe earthquake

early neoproterozoic sequence stratigraphy and acritarch biostratigraphy eastern officer basin south australia abstract the early neoproterozoic torrensian latest tonian 800 750 ma succession in the central and eastern officer basin was deposited in an intra cratonic rift basin the outcropping pindyin sandstone consists of basal lowstand conglomerate and upward fining transgressive sandstone and is conformably overlain by marine highstand shale of the alinya formation in the giles 1 well the pindyin sandstone contains aeolian to fluvial deposits and is overlain by peritidal and sabkha sediments of the alinya formation seismic interpretation suggests that the succession is thin on the murnaroo platform and thickens toward the munyarai trough the two sedimentary provinces are separated by the ungoolya hinge which probably marks the southeastern margin of the fraser musgrave fold belt highstand organic rich shale in the alinya formation is probably an important petroleum source rock acritarchs occur in both chert and shale in the alinya formation and their distribution was probably controlled by sedimentary environments similar assemblages from outcrop and subsurface provide a reliable evidence for regional correlation the assemblages in giles 1 are dominated by benthic coccoids and contain many distinct spinose acritarchs which are particularly abundant in the subtidal grey shale whereas mainly phytoplankton is present in the chert the assemblage represented by trachyhystrichosphaera vidalii t aimica cymatiosphaeroides kullingii can be used for global correlation in the early neoproterozoic the abundant microfossils from the alinya formation and equivalent beds around the world probably indicate a microorganism explosion at 750 800 ma prior to the neoproterozoic glaciations thirty seven acritarchs spheroids and seven cyanobacterial filaments are briefly described in this study including 5 new species comasphaeridium tonium eoentophysalis gilesis goniosphaeridium alinyum gorgonisphaeridium pindyium and gorgonisphaeridium torrensium and a newly combined species archaeoellipsoides karatavicus comb nov

sm nd and u pb zircon isotopic constraints on the provenance of sediments from the amadeus basin central australia evidence for ree fractionation abstract the amadeus basin of central australia is a late proterozoic to late palaeozoic ensialic depositional basin located between two proterozoic basement blocks of different nd crustal formation ages the older arunta block t dm nd 2 0 to 2 2 ga u pb zircon ages 1 5 1 9 ga to the north and the younger musgrave block t dm nd 1 7 to 1 9 ga u pb zircon ages 1 0 1 7 ga to the south initial nd isotopic compositions of the amadeus basin sediments generally fall into the region defined by the evolutionary trajectories of these two basement blocks indicating that the sediments are dominated by essentially two source components the older arunta block 147 sm 144 nd 0 114 and nd 0 20 4 and younger musgrave block 147 sm 144 nd 0 118 and nd 0 14 7 and or their equivalents stratigraphically higher sediments plot more closely to the evolutionary trajectory of the musgrave block this result together with the average provenance ages indicates the proportion of material from the musgrave block increases as the sediments become younger the sm nd isotopic data preclude a substantial involvement of archaean sources u pb zircon ion probe analyses of the late proterozoic heavitree quartzite and the late cambrian goyder formation are consistent with the sm nd isotopic constraints most of the zircons from the basal heavitree quartzite give concordant u pb zircon ages of 1500 to 1900 ma consistent with derivation from an arunta type source whilst zircons from the younger goyder sandstone give six discrete u pb zircon age groups of 511 20 615 15 960 109 1190 54 1633 24 and 1878 48 ma indicative of a dominantly musgrave type source with a minor contribution from the arunta block or reworked preexisting amadeus basin sediments the two youngest u pb zircon ages probably indicate some contribution from late proterozoic cambrian volcanics in central australia or a previously unrecognised younger local source in the basement blocks the 511 20 ma constrains the maximum depositional age of the sediment the amadeus basin sediments have a surprisingly wide range of 147sm 144nd ratios 0 077 0 136 irrespective of grain size and rock types in addition the calculated t dm nd values for samples from the same stratigraphic unit are well correlated with 147sm 144nd ratios with samples of different stratigraphic units forming sub parallel arrays these phenomena are interpreted in terms of ree fractionation and preferential sorting of preexisting ree rich phases during sedimentary recycling and deposition this process can lead to either an increase or a decrease in 147sm 144nd ratio of a sediment relative to its source and therefore an erroneous estimate of its t dm nd provenance age a theoretical model is developed which accounts for the observed correlation between t dm nd and 147sm 144nd ratios for suites of stratigraphically related sediments and allows a reliable estimate to be made of the provenance age of individual stratigraphic units assuming the average 147sm 144nd ratio of the source is known or can be estimated the provenance age for each stratigraphic unit of the amadeus basin has been calculated using this method the sm nd isotopic systematics in the amadeus basin sediments suggest that 1 1 ree fractionation during sedimentary recycling can in some cases be an important factor and needs to be considered 2 2 the provenance of the amadeus basin sediments was controlled by local source regions and cannot be used to infer large scale continental averages hence some caution must be evoked in using sm nd isotopic constraints from restricted sampling for more generalised models of crustal evolution

intracratonic strike slip partitioned transpression and the formation and exhumation of eclogite facies rocks an example from the musgrave block central australia mountain belts developed in an intracratonic setting during the neoproterozoic in the center of australia mesoproterozoic granulite and amphibolite facies gneisses of the musgrave block were overprinted during the petermann orogeny 550 ma with zones of high strain concentrated along broadly east west trending shear zones these zones formed under eclogite facies t 650 c and p 12 kbars to greenschist facies conditions and may form part of a strike slip related crustal scale flower type structure granulite facies gneisses preserve ages older than 700 ma suggesting that these rocks did not experience temperatures greater than 350 c at 550 ma for these rocks not to have been thermally equilibrated to temperatures of 350 c at a depth of 12 kbars requires either an extraordinarily low geothermal gradient 9 c km 1 or if the geothermal gradient was more typical 20 c km 1 then transport to that depth and subsequent exhumation occurring in a short time interval 40 myr

subdivision and correlation of late precambrian sequences in australia abstract the diversity of the australian precambrian record is used to empirically assess the application of all available techniques of correlation of late precambrian rocks lithofacies isotopic ages palaeontology and palaeomagnetism within the framework of latest lithostratigraphic geochronologic correlation charts lithostratigraphy is the main tool for intrabasinal correlation and mapping but isotopic ages will continue for some time yet to provide the main criteria for interregional correlation lithostratigraphic correlation is demonstrated over hundreds of kilometres but is generally constrained by tectonic controls to individual major crustal blocks climatic markers such as tillites may be correlated interregionally over thousands of kilometres the most exciting recent development in platform geochronology is the application of u pb zircon dating to fine grained tuffs illite may provide reliable minimum estimates but can be shown to be up to 150 ma too young glauconite and rb sr total rock shale ages have provided useful broad age estimates of sequences for which better methods are unavailable but only when based on cautious assessment and multiple sampling their ages may be either minimum or maximum stromatolites continue to demonstrate their potential for broad correlation when based on rigorous taxonomic study but the framework of time ranges of known taxa must be expanded for stromatolites to achieve their full potential especially for rocks older than 1000 ma acritarchs in black shales provide diverse and complex assemblages with excellent correlation potential but once again the australian taxonomic framework is still inadequate black cherts contain an evolutionarily conservative biota with only limited correlation potential recent palaeomagnetic studies based on both apwp and magnetostratigraphy demonstrate excellent potential for detailed correlations down to at least 1700 ma old however the present chronologically calibrated data base is sparse and must be supplemented by many more detailed studies through thick continuous rock sequences spanning substantial intervals of time the value of multidisciplinary correlation is elegantly demonstrated by very detailed and unambiguous correlation of combined palaeomagnetic isotopic age and stromatolite data across the 1700 ma mcarthur basin previous regional lithostratigraphic correlations have been conclusively and significantly revised with major implications to regional palaeogeography

the 2001 bhuj earthquake tomographic evidence for fluids at the hypocenter and its implications for rupture nucleation 1 the january 26 2001 bhuj earthquake mw 7 6 is one of the most catastrophic indian earthquakes we have investigated the 3 d seismic velocity and poisson s ratio structures of the bhuj source area to understand the probable cause of triggering the earthquake we used 1948 p and 1865 s wave high quality arrival times from 331 aftershocks recorded at a temporary seismic network significant variations up to 5 in velocity and 10 in poisson s ratio are revealed in the aftershock area the mainshock is located in a distinctive zone characterized by high vp low vs and high poisson s ratio in the depth range of 20 to 30 km and extending 15 to 30 km laterally this feature is very similar to that of the 1995 kobe earthquake zhao et al 1996 the anomaly may be due to a fluid filled fractured rock matrix which might have contributed to the initiation of the bhuj earthquake

timing and exhumation of eclogite facies shear zones musgrave block central australia timing constraints on shear zones can provide an insight into the kinematic and exhumation evolution of metamorphic belts in the musgrave block central australia granulite facies gneisses have been affected to varying degrees by mylonitic deformation some of which attained eclogite facies the davenport shear zone is a dominant strike slip system that formed at eclogite facies conditions t 650 c and p 12 0 kbar sm nd mineral isochrons obtained from equilibrated high pressure assemblages as well as 40ar 39ar data show that the eclogite and greenschist facies high strain overprints were coeval at c 550 ma mylonitic processes do not appear to have reset the u pb system in zircon but may have partially disturbed it the thermal gradient in the musgrave block crust at c 550 ma was c 16 c km 1 and at c 535 ma was c 18 c km 1 based on p t estimates of eclogite and greenschist facies shear zones respectively these estimates are similar to present day geothermal gradients in many stable continental shield areas suggesting that the region did not undergo a significant transient perturbation of the geotherm therefore in the musgrave block cooling subsequent to eclogite facies metamorphism appears to have been controlled by exhumation rather than by the removal of a heat source estimated exhumation rates in the range 0 2 to 1 5 mm year 1 are comparable with other orogenic belts rather than cratonic areas elsewhere

tectonic setting and provenance of the neoproterozoic uinta mountain and big cottonwood groups northern utah constraints from geochemistry nd isotopes and detrital modes abstract the neoproterozoic uinta mountain group was deposited in an east trending intracratonic rift bounded on the north by an active fault system and opening into a shallow sea on the west where the big cottonwood group was deposited in an estuary although this rift may have been associated with the early stages in the breakup of rodinia it was not an aulacogen geochemical nd isotope and detrital mode studies indicate that uinta mountain group sediments were derived from mixed archean and paleoproterozoic sources with the former dominating big cottonwood group sediments appear to have been derived predominantly from paleoproterozoic sources the archean sediment source is the wyoming craton and source rocks comprised dominantly granites enriched in th u y zr hf and ree the relative abundance of enriched granite implied by sedimentary rocks of the uinta mountain group indicates that the wyoming craton is anomalous compared to other archean cratons cia values and a cn k relationships in shales of the uinta mountain and big cottonwood groups indicate high degrees of weathering of sources probably in subtropical to tropical climates supporting a near equatorial location for southwestern laurentia at about 800 ma differences in the nd isotopic composition between the big cottonwood group and neoproterozoic sedimentary rocks in western utah and northeast nevada suggest a northwest striking uplift in northwest utah possibly ancestral to the paleozoic toole uinta arch

relationships between deformation and basin evolution in the intracratonic amadeus basin central australia abstract tectonic subsidence curves based on the sedimentary record are used here to study basin evolution and to indicate deformational periods in the history of the intracratonic amadeus basin in central australia the basin developed during an initial period of extension at about 900 ma in the late proterozoic stage 1 was subjected to another period of extension at about proterozoic cambrian boundary time when there was also a shortening event on the southwest margin stage 2 and was shortened during the late devonian early carboniferous stage 3 stage 1 extension in the southwest and northwest corners of the basin was associated with rift basin sediments and volcanics previously regarded as basement to the amadeus succession in the metamorphic arunta complex on the northern margin of the basin a dolerite dyke swarm is considered to have been emplaced during this event extension in a n s direction associated with stage 2 occurred only in the northern part of the basin at the same time a major compressional event the petermann ranges orogeny was occurring along the southern margin in the north the sediment fill at this time firstly thickens rapidly towards the northern margin and then thins dramatically at the margin implying a half graben structure and the presence of a major bounding fault in the southwest the petermann ranges orogeny caused detachment of the sediments above the salt horizon in the bitter springs formation northward transport folding of the sediment pile and formation of major basement cored nappes during stage 3 a foreland basin associated with southward directed overthrust sheets of the alice springs orogeny formed in the northern part of the basin horizontal shortening was of the order of 50 100 km and hence the present basin margins are structural rather than depositional the structures that developed during this stage dominate the structural pattern of the basin

nd isotopic and geochemical constraints on provenance of sedimentary rocks in the eastern officer basin australia implications for the duration of the intracratonic petermann orogeny sm nd isotopic and geochemical data from neoproterozoic to cambrian sedimentary rocks in the intracratonic eastern officer basin in central australia highlight the evolving provenance roles of the basement complexes that underlie and bound the basin initial e nd values of around 12 for the basal units indicate that both were largely derived from the late archaean to mesoproterozoic gawler craton which bounds the basin to the south at c 720 ma an influx of juvenile glacially derived sediment indicates partial uplift of the mesoproterozoic musgrave block along the basin9s northern margin in a regime interpreted to be broadly extensional at around 600 ma synchronous with the development of a foreland architecture there was a large influx of musgrave block derived sediments this is interpreted to mark the onset of the intracratonic petermann orogeny which was a long lived event or series of events spanning more than 70 ma subsequent to c 600 ma the nd isotopic composition of sequences within the officer basin indicates an increasing contribution from the gawler craton despite up to 45 km of denudation of part of the musgrave block this suggests that the majority of sediment derived from the petermann orogen bypassed the eastern officer basin for much of the history of the petermann orogeny

reservoir evaluation of the lower silurian longmaxi formation shale gas in the southern sichuan basin of china abstract the lower silurian longmaxi formation the palaeozoic is organic rich black shale in the southern sichuan basin the yangtze plate of china this study analyses the lateral extent and thickness burial depth total organic carbon content and thermal maturity of the longmaxi formation black shale as the key features of the shale gas reservoir the thickness of the black shale ranges from 10 to 170 m the thickest reservoir is located in changning naxi yongchuan region the toc of the shale at the bottom of the formation 50 m thickness is above 2 0 the lateral distribution of toc varies with the lateral distribution of thickness with the maximum toc in the gongxian luzhou yongchuan region the burial depth ranges from 2000 to 4500 m the shale is thermally over mature the evaluation of reservoir characteristics indicates that the longmaxi formation has conditions appropriate for shale gas accumulation and thus resource potential in the southern sichuan basin of china the objective of this preliminary evaluation of the reservoir characteristics is to locate potential areas favourable for exploration the most favourable areas are defined here as those where the thickness of black shale is more than 100 m and the burial depth is less than 3000 m these cover approximately 12 600 km 2 the most favourable areas which cover an area of approximately 5100 km 2 are located in the northeast luzhou region

temporal changes in nd isotopic composition of sedimentary rocks in the sevier and taconic foreland basins increasing influence of juvenile sources initial 143 nd 144 nd ratios of clastic sedimentary rocks in the ordovician taconic and sevier foreland basins increase with decreasing stratigraphic age this shift in isotopic composition reflects an increased influx of juvenile sediment to both basins for the taconic basin geologic and isotopic data are consistent with the juvenile sediment being derivedfromupliftedgrenvillecrust upthrustaspartofthetaconicallochthons sediment derivedfromthebronsonhillarc oracombinationofboth forthesevierforelandbasin there are few geologic constraints on source regions but the similar shift in isotopic ratios with time suggests a similar increase in the influence of juvenile sources such as exotic terranes sevier basin sedimentary rocks have higher nd values than those within the taconic basin thus juvenile source areas were of greater importance to sevier basin sediments

geochemical constraints on the growth of the continental crust several lines of evidence indicate that the archean upper crust was considerably more mafic than the present day upper crust there has been no significant change in ree and th abundances in post archean clastic sedimentary rocks suggesting that there has been no change in the composition of the upper crust during the post archean this indicates that if there have been any additions to the post archean upper crust they must have had similar composition to the upper crust itself geochemical modelling of ree and th abundances in sedimentary rocks suggests that the minimum ratio of post archean to archean upper crustal composition required to eliminate the archean upper crustal trace element signature within analytical uncertainty is about 4 1 such a model also is supported by isotopic data using plausible assumptions regarding the volume of archean crust isostatic relations and extreme models of the earth s degassing history it is proposed that approximately 65 75 of the continental crust formed