seismic structure of the longmenshan area in sw china inferred from receiver function analysis implications for future large earthquakes abstract following the 2008 mw 7 9 wenchuan and 2013 ms 7 0 lushan earthquakes the longmenshan thrust fault belt and the songpan ganzi terrane have been the focus of several investigations here we use the h k stacking technique and neighborhood algorithm to investigate the seismic structure of this area based on the presence of felsic lower crust and the mesozoic crustal architecture of the songpan ganzi and longmenshan area we exclude the model on the eastward flow of the middle and lower crust assigned as the cause for the crustal thickening in previous studies in contrast the e w trending cumulative compression induced by the continued northward motion of the indian plate and india asian collision are identified as the dominant factors leading to the crustal thickening in the longmenshan thrust fault region as well as the songpan ganzi terrane particularly the 2008 mw 7 9 wenchuan and 2013 ms 7 0 lushan earthquakes likely indicate the cumulative offsets and the e w continuing compression

density structure and isostatic state of the crust in the longmenshan and adjacent areas abstract in this study we ve analyzed some new gravity data obtained from two profiles across the longmenshan lms fault system in order to determine the density structure and isostatic state of the crust beneath the songpan ganzi block sg and the sichuan basin sc according to our research bouguer gravity anomalies along the two profiles range from 450 mgal in the sg to 80 mgal in the sc and density structural models show obvious differences between the sg and the sc compared with the sc the sg has lower average density in the crust and it has a low density layer with thickness of 5 km in the middle crust in the sc area however the crustal density increases gradually with depth and there exists no low density layer in the crust the moho interface decreases from 60 km beneath the sg in east tibet to 40 km beneath the sc in the lms region the topography bouguer gravity and moho depth change abruptly in a narrow tectonic belt the crustal isostatic state which is derived from the airy compensation model based on the topography gravity and deep seismic sounding data indicates that the sg on the northwest side of the lms is not in an isostatic state compared with the isostatic crust beneath the sc the isostatic equilibrium of the crust under the northeast section of the lms is not achieved as that in the southwest section of the lms based on the research we infer that the non homogenous collision between the tibetan plateau and the yangtze craton has caused the strong variation of the moho depth and the special isostatic state of the crust in this area

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

the origin and evolution of mineralizing fluids in a sediment hosted orogenic gold deposit ballarat east southeastern australia the hydrothermal fluids responsible for gold mineralization at the ballarat east gold deposit the second largest orogenic gold deposit in the western lachlan orogen are thought to have links to a variety of processes including metamorphism sedimentation and or magmatism in the current study noble gases and halogens have been used as fluid tracers to reevaluate the origin and evolution of the gold related fluids at the ballarat east deposit gold bearing quartz and carbonate veins from the ballarat east contain low salinity 4 wt nacl equiv aqueous h2o and mixed h2o co2 fluid inclusions these fluid inclusions have variable molar br cl values of between 1 2 10 3 and 2 9 10 3 and i cl values between 150 10 6 and 500 10 6 and br is strongly correlated with i defining a mixing line with a br i ratio of 5 6 the fluid inclusions have 40ar 36ar ratios ranging from 322 close to the atmospheric 40ar 36ar ratio of 296 up to a maximum of 4503 40ar is strongly correlated with cl and defines a mixing line with a 40are cl ratio of 4 6 10 4 40are denotes excess 40ar the fluid inclusions contain 5 1 to 32 ppm 40are by mass and exhibit minimum 36ar concentrations ranging from 3 1 to 11 ppb which exceed air saturated water asw levels by several parts per billion asw 1 3 2 7 ppb fluid inclusion 84kr 36ar and 130xe 36ar values are uniformly enriched in kr and xe relative to air but exhibit limited variation these data provide strong evidence for the involvement of two noble gas and halogen reservoirs this data is compatible with a deeply sourced fluid possibly originating by devolatilization of altered volcanic rocks e g basalts that acquired additional noble gases and organic br plus i by interaction with sedimentary rocks including organic rich shales that are found beneath and surrounding the deposit the data are also consistent with mixing deeply sourced metamorphic fluids with sedimentary formation waters however both interpretations favor the involvement of metamorphic fluids and sedimentary components and highlight the significance of fluid rock interaction as controls on fluid compositions in victorian deposits the data are compatible with genetic models for orogenic gold in which gold mineralization was initiated by metamorphic devolatilization in the lower crust and was linked to lachlan orogenesis at ca 440 ma

co seismic ruptures of the 12 may 2008 ms 8 0 wenchuan earthquake sichuan east west crustal shortening on oblique parallel thrusts along the eastern edge of tibet abstract the m s 8 0 wenchuan earthquake which devastated the mountainous western rim of the sichuan basin in central china produced a surface rupture over 200 km long with oblique thrust dextral slip and maximum scarp heights of 10 m it thus ranks as one of the world s largest continental mega thrust events in the last 150 yrs field investigation shows clear surface breaks along two of the main branches of the ne trending longmen shan thrust fault system the principal rupture on the nw dipping beichuan fault displays nearly equal amounts of thrust and right lateral slip basin ward of this rupture another continuous surface break is observed for over 70 km on the parallel more shallowly nw dipping pengguan fault slip on this latter fault was pure thrusting with a maximum scarp height of 3 5 m this is one of the very few reported instances of crustal scale co seismic slip partitioning on parallel thrusts this out of sequence event with distributed surface breaks on crustal mega thrusts highlights regional ew directed present day crustal shortening oblique to the longmen shan margin of tibet the long rupture and large offsets with strong horizontal shortening that characterize the wenchuan earthquake herald a re evaluation of tectonic models anticipating little or no active shortening of the upper crust along this edge of the plateau and require a re assessment of seismic hazard along potentially under rated active faults across the densely populated western sichuan basin and mountains

hydrothermal alteration in metasedimentary rock hosted orogenic gold deposits reefton goldfield south island new zealand orogenic or mesothermal quartz lodes in lower palaeozoic greenland group metasedimentary rocks of the reefton area have produced 67 tonnes t of gold prior to 1951 and recent exploration has identified new gold resources in several deposits including the largest past producers blackwater and globe progress the metasedimentary rocks consist of alternating sandstone and mudstone beds that were metamorphosed to lower greenschist facies prior to being hydrothermally altered adjacent to the quartz lodes the sandstones are feldspathic litharenites averaging q65 f10 r25 with detrital grains of quartz rock fragments muscovite and plagioclase and biotite that were altered to albite and chlorite respectively during metamorphism accessory minerals are graphite apatite zircon tourmaline and titanite hydrothermal alteration of the sandstones has developed a mineral assemblage of k mica carbonate dolomite ankerite ferroan magnesite and magnesian siderite chlorite pyrite and arsenopyrite the abundance of hydrothermal chlorite is greater at blackwater than at the other prospects studied hydrothermal alteration associated with the quartz lodes is marked by bleaching magnesian siderite spots disseminated arsenopyrite and pyrite and thin carbonate quartz and sulphide veins these trends are accompanied by increasing concentrations of s as and sb and decreasing na and a decrease of fe and mg in k mica the alkali alteration indices 3k al representing k mica and na al representing albite generally show antipathetic trends with 3k al increasing near the lodes and na al decreasing these trends reflect the replacement of albite by k mica carbonate alteration indices co2 ca mg fe and co2 ca mg fe 0 5 s as quantify the abundance of hydrothermal carbonates but they show variable correlation with the lodes they increase the width of the alteration halo in the hanging wall of the lodes at the globe progress and general gordon prospects but the peak values are as far as 150 m from the lodes by contrast peak values of the carbonate alteration indices are within 10 and 2 m of the lodes respectively at the merrijigs and blackwater deposits data show that for deposits with wide hydrothermal alteration halos such as at the globe progress and general gordon prospects the use of a suite of geochemical indicators can assist exploration by indicating trends in hydrothermal alteration that provide vectors to mineralisation they also increase the size of the exploration target by contrast the alteration halo of the blackwater deposit is restricted to within less than 5 m of the quartz lode and therefore the geochemical indicators are of more limited assistance to exploration

structural controls on tertiary orogenic gold mineralization during initiation of a mountain belt new zealand two types of structurally controlled hydrothermal mineralization have occurred during folding of fissile schist in southern new zealand fold related mineralization and normal fault related mineralization both types have the same mineralogy and textures and are dominated by quartz ankerite veins and silicified breccias with ankeritic alteration most mineralized zones are thin centimetre scale although host schist is commonly impregnated with ankerite up to 20 m away thick up to 5 m wide mineralized zones are generally gold bearing and contain pyrite and arsenopyrite with stibnite pods locally some of these auriferous zones have been extensively mined historically despite rugged topography and difficult access mineralization occurred during regional tectonic compression in the initial stages of development of the southern alps mountain belt at the pacific australian plate boundary in the miocene most of the gold bearing deposits occur in east to south east striking normal faults that cut across mesoscopic folds in a belt that coincides with the southern termination of a regional scale north trending antiform mineralized zones have similar structural control and relative timing to a nearby swarm of miocene lamprophyre dykes and carbonatites limited stable isotopic data c and o and trace element geochemistry suggest that there was probably no genetic link between the igneous activity and gold mineralization however these two types of fluid flow have been controlled by the same tectonically created crustal plumbing system this miocene hydrothermal activity and gold deposition demonstrates that orogenic mesothermal mineralization can occur during the inception of an orogenic belt not just in the latter stages as is commonly believed these miocene structures have been preserved in the orogen because the locus of uplift has moved northwards so the early formed gold deposits have not yet been structurally overprinted or eroded

the hengshan low angle normal fault zone structural and geochronological constraints on the late mesozoic crustal extension in south china abstract we document in this paper a significant low angle normal fault namely the hengshan detachment fault which extends more than 150 km long in nne orientation and bounds an elongated early cretaceous basin in hunan province central south china detailed structural and geochronological analyses have been conducted along its southern segment where a well exposed 3 km thick flat ductile shear zone develops along the western margin of the hengshan granitic massif this zone is featured by shallow dipping foliations of varied trend from ne to nw which bear penetrative stretching lineations varying from nw to sw trend shear sense criteria indicate top to the nw and top to the sw motions along its northern and southern parts respectively quartz c axis orientations of mylonitic rocks from the shear zone exhibit asymmetric single or crossed girdle patterns and the distributions of fabric point maxima suggest a simultaneous operation of basal and prism slips indicating a deformation temperature ranging from 400 c to 550 c one zircon u pb age of the sheared albitite and three muscovite 40 ar 39 ar ages of the mylonitic rocks indicate that the ductile shearing initiated at 136 ma and lasted till 97 ma the zircon u pb dating results of five granitic samples from the hengshan granitic pluton yield two phases of crystallization ages of 232 228 ma and 150 151 ma respectively indicating two preceding magmatic events prior to the ductile shearing in the lower plate our structural and geochronological data allow defining the hengshan massif as an extensional dome rather than a metamorphic core complex as previously predicted due to the lack of syn tectonic plutonism and the origin of detachment fault associated with the reactivation of the inherited thrust this study provides crucial evidence for understanding how the mid upper crust deformed during the process of extension which testifies to a coeval occurrence of non coaxial deformation of the ductile flow in the middle crust and brittle faulting in the upper crust it also sheds new insights into the timing of the regional crustal extension in south china and permits to constrain its onset time to be ca 136 ma

crustal structure of chuan dian region derived from gravity data and its tectonic implications abstract in this paper bouguer gravity data were used to invert crustal structure of the chuan dian region of china both multi scale wavelet analysis and density interface inversive methods were adopted three gravity models transverse to major blocks were constructed our research indicates that great differences exist in crustal structures between the eastern basin and the western plate and crustal structures of chuan dian region are closely correlated with tectonic activities of the eastern tibetan plateau the western sichuan platform experienced strong deformation due to eastward extrusion of the tibetan plateau this led to heaving of the upper crust and thickening of the lower crust the low density crusts of western blocks were deformed by many high angle faults and most of these faults cut through to the middle crust density structures of upper and middle crusts are restricted by the regional tectonic stress fields and fault zones the lower crust was deformed by folding inducing high and low density anomalies alternatively rocks beneath the longmenshan sub block and the northwestern sub block of sichuan were severely broken for strong eastward extrusion of the plateau large areas of low density anomaly were observed in the lower crust adjusted by gravity isostasy the lower crusts of the chuan dian block and the songpan garze block have thickened intensely density structures present highly inhomogeneous manner in lateral direction throughout the western block crustal densities of the sichuan basin are much more homogeneous and the whole lithosphere is denser than that of western block in transitional area between the south china block and the chuan dian block with the decreasing of crustal density crustal stability is also depressed in addition we obtained a detailed map of moho using variable density model the moho topography undulates greatly beneath the chuan dian region the maximum crustal thickness difference of the chuan dian region is about 30 km moho depth across longmenshan descends from 43 km in the east to nearly 60 km in the west the maximum and minimum moho depths of the western blocks are about 65 and 46 km in the litang area and in the panzhihua area respectively structural directions of moho topography are consistent with strikes of fault tectonics

gravity field and deep seismogenic environment in the longmen shan and adjacent regions eastern tibetan plateau abstract in this paper we adopt the methods of euler deconvolution source parameter imaging spi source edge detection sed inversion of the moho interface and three dimensional 3 d visualization of the crust for the inversion of the bouguer gravity anomaly of the longmen shan and adjacent regions analyse the 3 d structure deep structure and deformation characteristics of the crust and investigate the cause of the deep seismogenic environment and the wenchuan earthquake the research indicates that the longmen shan fault zone is characterized by a ne trending large gravity gradient zone with a gradient value that exceeds 3 7 mgal km the euler diagram reveals that there is a low density anomaly body in the lower crust of the longmen shan fault zone that is a ne trending narrow strip approximately 100 km long 65 km wide and 35 50 km deep the songpan garze block on the northwest side does not have the material source and pathway of the lower crustal flow in the euler diagram therefore the low density anomaly body is related to the upwelling of the mantle heat flow below it in comparison with the songpan garze and chuan dian blocks the strength of the field source of the sichuan basin is high 175 to 96 mgal indicating that the average density of the crust is high and the depth of the field source is stable at 15 25 km the sed map reveals that there has been counter clockwise rotation of the sichuan basin since the cenozoic the spi shows that the longmen shan fault zone is narrowly located in the beaded linear shallow source anomaly belt and that its two sides are stable areas of deep source anomalies indicating characteristics of crustal hardness on both sides so that it is prone to accumulate stress and strain the moho depth across the longmen shan descends from 41 8 km in the east to 61 6 km in the west the complex intersection of high density and low density anomaly bodies appears in the deep part of the longmen shan tectonic belt and the crustal structure is fragmented moreover there is a strong abrupt change in the moho topography and therefore this region has a deep environment for the genesis of strong earthquakes the dextral strike slip movement of the longmen shan fault zone is caused by the movement of the songpan garze block and the counter clockwise rotation of the sichuan basin therefore the counter clockwise rotation of the sichuan basin is one of the important dynamic backgrounds for the 2008 wenchuan earthquake

architecture of basin mountain systems and their influences on gas distribution a case study from the sichuan basin south china abstract the basin mountain systems in the sichuan basin exert major control on today s oil gas distribution chiefly through their controlling influence on petroleum reservoirs preservation the thickness of deposited terrestrial formations and degree of uplift and denudation the composite basin mountain system in the sichuan basin and its peripheral mountains can be classified as two types margin plate systems and interior plate systems the margin plate basin mountain systems include the sichuan basin and its surrounding longmen mountains micang mountains and daba mountains which are not only the western and northern marginal area of the sichuan basin but also represent the western margin of the yangtze plate south china block the margin plate basin mountain systems with binary units of large scale thrust belts and foreland basins have different deep lithospheric structures abrupt boundaries and great contrast in today s geomorphology between the basin and the mountains on the contrary the interior plate basin mountain systems comprised by the sichuan basin and its adjacent interior plate qiyue mountains dalou mountains and daliang mountains represent the eastern and southern marginal area of the sichuan basin located within the yangtze plate they have similar lithospheric structure and gradual boundaries between the basin and the adjacent mountains lacking foreland basins today s medium large scale natural gas accumulations in the sichuan basin are mainly distributed in the areas influenced by the margin plate basin mountain systems and are located especially in the foreland basins

relationship between characteristics of gravity and magnetic anomalies and the earthquakes in the longmenshan range and adjacent areas abstract the 2008 wenchuan earthquake and aftershocks occurred along the northeast trending longmenshan fault zone in the eastern margin of the tibetan plateau the tibetan plateau has the strongest negative bouguer gravity anomaly zone in china and is surrounded by the great gravity horizontal gradient belt the horizontal gradient belt of the observed gravity anomaly in the longmenshan area is a part of this giant gravity gradient belt the longmenshan fault zone is located to the east of this belt the horizontal gradient belt of the residual gravity anomaly obtained by removing large effects of sedimentary basin and variations in the crustal thickness well matches the longmenshan fault zone but this belt is located to the east of the horizontal gradient belt of the observed gravity anomalies the deviation of the two horizontal gradient belts increases from the southwest to the northeast with a maximum of about 40 50 km a significant difference in density exists in the lower crust and the uppermost mantle between the songpan ganze block and the sichuan basin block the songpan ganze block is less dense than the sichuan basin block in the lower crust as well as in the uppermost mantle the boundary between the two blocks is located to the west of the wenchuan maoxian yinxiu beichuan and anxian guanxian faults approximately the fault plane crosses the lower crust and uppermost mantle the rigid sichuan basin block acts as a resistant for the pushing from the songpan ganze block far field effects of the collision between the indian and eurasian plates might lead to thrust of some brittle layers in the upper crust along the detachment in the middle crust of the songpan ganze block when movement on a large and deep crustal mega thrust occurs earthquakes strike the longmen shan margin of the tibetan plateau in the guanxian beichuan segment in the southern longmenshan fault zone push from the songpan ganze block is perpendicular to the density boundary which corresponds to the location of the horizontal gradient belt of the residual gravity but in the guanxian beichuan segment in the northern longmenshan fault zone the push is oblique to the location of this gradient belt such a relationship could lead to nearly equal amounts of thrust and right lateral slip along the beichuan qingchuan segment and in contrast to nearly pure thrust along the guanxian beichuan segment an unusually large negative magnetic anomaly occurs around qingchuan wenchuan guanxian the computed magnetic model shows that some crystalline complexes with reversal magnetization might exist in the crust which might be related to extrusion of the metamorphic basement rocks in the lower to middle crust

utilization of pre existing competent and barren quartz veins as hosts to later orogenic gold ores at huangjindong gold deposit jiangnan orogen southern china most if not all orogenic gold deposits form during the late stages of deformation in some cases there is barren pre mineralization hydrothermal alteration which may be part of a single progressive hydrothermal event or a temporally distinct event relative to deposition of gold at the huangjindong orogenic gold deposit in the jiangnan orogen of southern china there are two phases of vein generation the earlier of which is largely barren structural analysis petrography mineralogy and in situ laser ablation inductively coupled plasma mass spectrometry la icp ms gold mapping of different generations of gold bearing sulfides reveal the relationship between different phases of hydrothermal alteration and quartz veins pre existing barren and brittle quartz veins which are controlled by tight folds and thrust faults provide favorable competent hosts for later overprinting by gold bearing ore bearing fluids that infiltrated during ongoing reverse sinistral fault movement these overpressured fluids caused hydrofracturing to complete brecciation of segments of the earlier quartz veins and associated pre existing breccias with deposition of auriferous quartz sulfide veins and breccia cements or matrices within them although fluid inclusion data are non definitive fluid pressure fluctuations are interpreted to have resulted in phase separation within the ore fluid which was primarily responsible for destabilization of gold complexes and deposition of native gold with other invisible gold bearing ore related sulfides formed by sulfidation reactions in hydrofractures and breccia matrices thus competent barren quartz veins in fold thrust belts may locally host superimposed gold mineralization and provide favorable targets for gold resources

the bronzewing lode gold deposit western australia p t x evidence for fluid immiscibility caused by cyclic decompression in gold bearing quartz veins abstract the bronzewing lode gold deposit is located in the yandal greenstone belt in the yilgarn craton of western australia gold mineralization is hosted in tholeiitic basalt that is metamorphosed to greenschist facies individual ore bodies are controlled by a complex gold bearing quartz vein system that comprises shear and extension veins formed during a progressive d2 deformation event gold is localized in quartz along fractures and deformed grain boundaries and is interpreted to have formed late in the formation of the veins detailed petrography and microthermometry on primary pseudosecondary and secondary fluid inclusions trapped in gold bearing shear and extension veins revealed five types of fluid inclusions 1 co2 ch4 h2o nacl inclusions of variable salinity 0 1 to 17 5 eq wt nacl containing between 10 and 99 mol co2 and molar volumes that range from 22 to 76 cm3 2 h2o nacl inclusions of variable salinity 0 4 to 22 1 eq wt nacl 3 co2 ch4 inclusions with up to 58 mol ch4 and molar volumes between 54 and 73 cm3 4 ch4 h2o inclusions with ch4 ranging from 80 to 90 mol and 5 ch4 inclusions with low molar volumes of 19 to 23 cm3 types 1 2 and 3 constitute a fluid inclusion assemblage that occurs consistently in primary pseudosecondary and secondary trails and clusters within the gold bearing quartz vein system these co existing fluids are interpreted to have formed by fluid immiscibility of a low salinity homogeneous parent fluid at about 300 c and 1500 bars locally type 2 fluid inclusions exhibit total homogenization temperatures that are on average 100 c less than the co genetically trapped type 1 aqueous carbonic inclusions this discrepancy is interpreted to have involved co2 effervescence in response to fluid pressure fluctuations types 4 and 5 fluid inclusions are rare and are only present locally in secondary trails and clusters in extension veins significant pressure fluctuations but relatively constant homogenization temperatures for types 1 2 and 3 fluid inclusions suggest that cyclic decompression of the hydrothermal fluids due to seismic activity along the shear zones that host the gold bearing veins triggered fluid immiscibility the process of fluid immiscibility and subsequent lowering of gold solubility is interpreted to be the most efficient precipitation mechanism for gold in the d2 shear zone hosted vein system at bronzewing

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

mineral precipitation in the quartz reefs of the bendigo gold deposit victoria australia gold precipitation at bendigo postdates cleavage development and was initiated during folding increased during a reverse faulting stage in bedding parallel quartz veins and culminated in quartz reefs associated with a strike slip faulting event some gold was remobilized along carbonate rich cataclasites associated with later brittle faults understanding the paragenesis of the sulfide and gangue minerals associated with the auriferous quartz reefs is critical to unraveling the cycle of ore genesis from source to sink in this study a petrographic approach closely tied to macroscopic structural observations along with stable isotope and fluid inclusion analyses places constraints on the relative timing of gold mineralization with respect to deformation early sulfide assemblages in bedding and cleavage parallel veins are dominated by pyrite pyrrhotite siderite and are free of visible gold later assemblages in reactivated bedding parallel veins and other fold related veins are characterized by the presence of arsenopyrite ankerite gold fault related veins and the massive quartz reefs are rich in sphalerite and galena with associated gold but lack pyrrhotite small amounts of late stage antimony bearing minerals occur in many vein types and postdate the precipitation of gold decreasing temperature and increasing sulfur activity controlled successively younger sulfide assemblages in the quartz veins stable oxygen isotope data show that quartz from all vein types 18 o 15 9 19 0 homogenized with the host rocks whereas carbon 13 c 14 0 to 4 1 and oxygen 18 o 4 5 24 0 in carbonate have a wider range in values that is interpreted to be a function of decreasing temperature this corresponds with early siderite pyrrhotite and anhedral pyrite and with later ankerite and ferroan dolomite associated with arsenopyrite galena and euhedral pyrite that are crosscut by calcite veins fluid inclusions in quartz veins are predominantly composed of water with carbon dioxide with smaller proportions of nitrogen and methane particularly in the later strike slip faults the sporadic occurrence of methane suggests that there was an open fluid system with incoming fluids from an external source mixing with those in the host rocks although several recent studies have argued that synsedimentary preenrichment may be a significant factor determining the size and distribution of gold in the bendigo orogenic gold deposits we believe there is little direct or deposit scale evidence for a relationship between original metal content in the host rock metasedimentary rocks and the distribution of the gold mineralization in specific structural sites it is suggested that deep seated faults act as conduits for fluid flow and the source for the gold at bendigo the gold is externally derived from deeply sourced auriferous metamorphic fluids that have been focused into discrete structural sites

the structural setting and contact metamorphism of the wonga gold deposit victoria australia gold quartz vein deposits in the wonga mine area are fault related structures occur in a low grade regionally metamorphosed cambrian quartz rich turbidite sequence wonga schist interlayered with mafic volcanics and postdate a suite of quartz feldspar porphyry dikes the nonplanar geometry of these vein deposits can be explained by their location within a shear system as en echelon dilations in combination with refraction across rheological interfaces within the sediment package the gold mineralization and related deformation occurred under low to midgreenschist facies conditions the intrusion of the early devonian stawell granite at approximately 400 ma has contact metamorphosed the wonga schist a preexisting suite of porphyry dikes and the first stage of mineralization typically mineralization and alteration occur in discrete dilational openings as a package of mineralized structures related to a d 4 deformation event and fluid injection the first stage of gold mineralization and accompanying alteration was deposited in 350 degrees trending 25 degrees to 50 degrees east dipping fracture sets within a 320 degrees trending shear system eastern and western shears and a 240 degrees trending 40 degrees to 70 degrees southeast dipping extensional fracture set link structures both the eastern and western shears are anastomosed high strain zones up to 50 m in width and are connected at a high angle by linking mineralized structures that begin to dominate as the main mineralized lodes persist with depth where the mineralized link has an east west trend the lodes located within the eastern and western shear zones are oblique shear veins whereas the link structures are large scale tensile fractures in the block between the zones of shear zone hosted mineralization these d 4 features initiated in a regional northeast southwest crustal shortening episode subsequent deformation was then accommodated by sinistral oblique slip during a north south compressional event the mineralized lodes are locally influenced by a set of northwest trending shallow northeast dipping faults and refracted across the preexisting porphyry dikes postdating the stawell granite is a second stage of hydrothermal fluid introduction along some northwest trending northeast dipping faults d 5 event this fluid flow is focused along the reverse faults and gave rise to local retrogression of peak contact metamorphic assemblages producing local carbonate sericite alteration and further gold mineralization subsequent fluid activity has produced carbonate alteration and or minor sulfide mineralization that can be related to either the stawell granite late fractures or a suite of lamprophyre dikes

the location and evolution of the tectonic boundary between the paleoproterozoic jiao liao ji belt and the longgang block northeast china abstract in this paper we discuss the location nature and evolution of the tectonic boundary between the jiao liao ji belt and the longgang block northeast china the boundary in terms of paleogeography which involves a study of the liaohe group or tectonics employing non seismic geophysical data e g gravity data and magnetotelluric soundings existing geological data and the differences in physical properties between the jiao liao ji belt and the longgang block we clarified the spatial distribution of the tectonic boundary and characterized the geological bodies at different depths on either side of the boundary we analyzed the most recently updated bouguer gravity anomaly gravity magnetic and electrical profile data as well as comprehensive data on the physical properties of the rocks in the research area thus providing information on the geological nature of the boundary at deep levels the results indicate that during the early period of formation of the jiao liao ji belt a basin controlling boundary fault developed that constituted the original tectonic boundary between the jiao liao ji belt and the longgang block this fault extended from shuangtaling to sandaoling lian shanguan dawanggou balidianzi and erhulai to guaimozi following a roughly east west trend most previous studies have considered that the liaohe group which extends from benxi city to benxi county and huanren county is the paleo geographic boundary of the jiao liao ji belt

rapid dewatering of the crust deduced from ages of mesothermal gold deposits the large scale migration of fluids through the continental crust has been well documented but there is no consensus regarding the timing of fluid migration relative to orogenic episodes or rates of crustal dewatering1 here we present40ar 39ar dates for muscovites from quartz veins along a major shear zone in southeast alaska which show that the veins were emplaced in the early eocene during the late stages of orogenic deformation hydrother mal activity took place for only about 1 myr and along a distance of at least 200 km the fluids were generated by metamorphic reactions in subducted crust along the north american plate margin and were apparently trapped in the crust by the low permeabilities accompanying a convergent tectonic regime until 56 myr ago the rapid dewatering event coincided with a change in plate motion at 56 55 myr which caused a shift from convergent to partly transcurrent tectonics we suggest that this change in tectonic regime led to increased crustal permeabilities and hence the possibility of large scale fluid migration

seismically constrained thermo rheological structure of the eastern tibetan margin implication for lithospheric delamination article i nfo the eastern tibetan margin bordered by the longmen shan range exhibits significant lateral differences in the lithospheric structure and thermal state to investigate the roles of these differences in mountain building we construct a thermo rheological model along a wide angle seismic profile across the eastern tibetan margin based on recent seismic and thermal observations the thermal modeling is constrained by the surface heat flow data and crustal p wave velocity model the construction of the rheological envelopes is based on rock me chanics results and involves two types of rheology a weak case where the lower crust is felsic granulite and the lithospheric mantle is wet peridotite and a strong case where the lower crust is mafic granulite and the litho spheric mantle is dry peridotite the results demonstrate 1 one high temperature anomaly exists within the uppermost mantle beneath eastern tibet indicating that the crust in eastern tibet is remarkably warmer than thatinthe sichuanbasin and 2 therheologicalstrengthofthe lithosphericmantlebeneatheasterntibetiscon siderably weaker than that beneath the sichuan basin the rheological profiles are in accord with seismicity dis tribution by combining theseresults with the observed crustal lithospheric architecture pn velocity distribution and magmatism in the eastern tibetan margin we suggest that the delamination of a thickened lithospheric mantle root beneath eastern tibet is responsible for the growth of the eastern tibetan margin

a gravity study along a profile across the sichuan basin the qinling mountains and the ordos basin central china density isostasy and dynamics abstract in order to investigate the structure of the crust beneath the middle qinling mountains mql and neighboring areas in the north china block and south china block a north south gravity profile from yuquan in the sichuan basin to yulin in the ordos basin was conducted in 2011 the bouguer gravity anomaly is determined from a high quality gravity dataset collected between 31 n and 36 n of latitude and varies between 200 and 110 mgal in the study region using accredited velocity density relationships an initial crust mantle density model is constructed for mql and adjacent areas which is later refined interactively to simulate the observed gravity anomaly the present study reveals the features of the density and bouguer gravity with respect to the tectonic units sampled by the profile the lithosphere density model shows typical density values that depict a layered structure and allow differentiate the blocks that extend along the reference profile the gravity field calculated by forward modeling from the final density distribution model correlates well with the measured gravity field within a standard deviation of 1 26 mgal the density in the crystalline crust increases with depth from 2 65 g cm3 up to the highest value of 2 95 g cm3 near the bottom of the crust the conrad interface is identified as a density jump of about 0 05 g cm3 the average density of the crust in mql is clearly lower than the density in the formations on both sides starting from a combined airy pratt isostatic compensation model a partly compensated crust is found below mql suggesting future growth of the crust unlike the ordos and sichuan basins that will remain stable on the basis of the density and isostatic state of the crust and additional seismological research such as the p wave velocity model and poisson s ratio it is concluded that the lower crust delamination is a reasonable interpretation for the geophysical characteristics below the qinling orogen

fluid infiltration into fault zones chemical isotopic and mechanical effects fluid infiltration into fault zones and their deeper level counterparts brittle ductile shear zones is examined in diverse tectonic environments in the 2 7 ga abitibi greenstone belt major tectonic discontinuities with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism during reverse motion on the structures accommodating shortening of the belt these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids such fluids were characterised by 18o 6 2 d 50 20 13c 4 4 and temperatures of 270 to 450 c probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism hydrothermal fluids were more radiogenic 87sr 86sr 0 7010 to 0 7040 and possessed higher than did contemporaneous mantle komatiites or tholeiites and thus carried a contribution from older sialic basement a provinciality of87sr 86sr and 13c is evident signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres mineralised faults possess enrichments of large ion lithophile lil lil elements including k rb ba cs b and co2 and rare elements such as au ag as sb se te bi and w fluids were characterised by xco2 0 1 neutral to slightly acidic ph low salinity 3 wt k na 0 1 they carried minor ch4 co and n2 and they underwent transient effervescence of co2 during decompression clastic sediments occupy graben developed at fault flexures the40ar 39ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years

gold ore forming fluids of the tanami region northern australia fluid inclusion studies have been carried out on major gold deposits and prospects in the tanami region to determine the compositions of the associated fluids and the processes responsible for gold mineralization pre ore milky quartz veins contain only two phase aqueous inclusions with salinities 19 wt nacl eq and homogenization temperatures that range from 110 to 410 c in contrast the ore bearing veins typically contain low to moderate salinity 14 wt nacl eq h2o co2 ch4 n2 bearing fluids the co2 bearing inclusions coexist with two phase aqueous inclusions that exhibit a wider range of salinities 21 wt nacl eq post ore quartz and carbonate veins contain mainly two phase aqueous inclusions with a last generation of aqueous inclusions being very cacl2 rich salinities range from 7 to 33 wt nacl eq and homogenization temperatures vary from 62 to 312 c gold deposits in the tanami region are hosted by carbonaceous or iron rich sedimentary rocks and or mafic rocks they formed over a range of depths at temperatures from 200 to 430 c the groundrush deposit formed at the greatest temperatures and depths 260 430 c and 11 km whereas deposits in the tanami goldfield formed at the lowest temperatures 200 c and at the shallowest depths 1 5 5 6 km there is also evidence in the tanami goldfield for late stage isothermal mixing with higher salinity 21 wt nacl eq fluids at temperatures between 100 and 200 c other deposits e g the granites callie and coyote formed at intermediate depths and at temperatures ranging from 240 to 360 c all ore fluids contained co2 n2 ch4 with the more deeply formed deposits being enriched in ch4 and higher level deposits being enriched in co2 fluids from deposits hosted mainly by sedimentary rocks generally contained appreciable quantities of n2 the one exception is the tanami goldfield where the quartz veins were dominated by aqueous inclusions with rare co2 bearing inclusions calculated 18o values for the ore fluids range from 3 8 to 8 5 and the corresponding d values range from 89 to 37 measured 13c values from co2 extracted from fluid inclusions ranged from 5 1 to 8 4 these data indicate a magmatic or mixed magmatic metamorphic source for the ore fluids in the tanami region interpretation of the fluid inclusion alteration and structural data suggests that mineralization may have occurred via a number of processes gold occurs in veins associated with brittle fracturing and other dilational structures but in the larger deposits there is also an association with iron rich rocks or carbonaceous sediments suggesting that both structural and chemical controls are important the major mineralization process appears to be boiling effervescence of a gas rich fluid which leads to partitioning of h2s into the vapor phase resulting in gold precipitation however some deposits also show evidence of desulfidation by fluid rock interaction and or reduction of the ore fluid by fluid mixing these latter processes are generally more prevalent in the higher crustal level deposits

structural constraints and numerical simulation of strain localization in the bendigo goldfield victoria australia strain localization and fluid flow patterns adjacent to the massive quartz hosted reefs of the bendigo gold field have been investigated using new structural observations three dimensional geometry of fold fault relationships and gold distribution quartz reef and vein formation in the bendigo goldfield is associated with an initial e w compression event that produced a penetrative upright cleavage and n s trending fold hinges in the immediate hanging wall of quartz reefs with high gold grades the s1 cleavage is locally deformed by an e w trending s2 cleavage that is attributed to a low strain n s oriented compressive event further evidence of this low strain event is provided by gently s plunging quartz carbonate slickenline lineations on s1 cleavage surfaces and the reef margin surfaces and visible gold within the outer portions of the reef the reefs are commonly situated on or immediately to the south of a left flex sinistral change in strike of the axial surface of the folds and the flexure occurs close to an anticlinal culmination defined by the double plunging n s striking folds the folds become deformed with meter to decimeter wavelengths which generally affect the stiff units in a disharmonic style accompanying this is a reactivation of reef margins by oblique slip and the formation of dilational sites and tensional vein arrays that provide the conduits for fluid flow and gold deposition numerical models that best simulate the observed distribution of strain based upon the location of quartz reefs involve nw se oriented contraction with a significant sinistral strike slip component this contraction event has an overall n s sense orientation and is therefore consistent with deformation features in the immediate hanging wall of quartz reefs the models also demonstrate a geometrical dependence on the localization of strain and thus the potential localization of fluid flow volume and shear strain increase with the flex angle and variations in the magnitude of strain are also associated with variations in the strike angle of the flexure this analysis highlights that the modification of preexisting fold structures and quartz veins by a low strain event may enhance the localization of dilation sites within individual quartz reefs where there are subtle changes in the orientation of the reef margins such numerical modeling can also improve ranking of exploration targets based on fold geometry and provide a better understanding of fluid flow in hydrothermal mineral systems

crustal scale tectonic wedging in the central longmen shan constraints on the uplift mechanism in the southeastern margin of the tibetan plateau abstract this study focuses on the upper middle crust umc deformation in the central longmen shan lms the results of this study are constrained by the surface geology typical seismic reflection profiles previously available thermochronology and deep geophysical data regional seismic profiles demonstrate a strata dip of about 2 northwest trending from the sichuan basin sb to lms the interpretation of shallow artificial seismic reflection data indicates that an unknown basement structure lead to the uplifting of the sedimentary cover by 3 4 km a long and wide angle reflection seismic profile presents evidence that the middle crustal scale structure is involved in the deformation geophysical data support that there is an upper detachment d1 at the depth of 20 km the other lower detachment d2 could be generated at approximately 30 40 km depth in the low velocity zone the ductile middle crust between the d1 and d2 has shortening and forming a wedge tip beneath the transition zone of the lms and the sb the deformation of the lms frontal monocline belt is related to this crustal scale wedging two different tectonic stages are distinguished in the cenozoic through the axial surface analysis and chronological data during the first stage the crustal scale tectonic wedge was developed between the upper and lower detachment resulting in the uplift of the umc during the second stage the middle crust could hardly be extruding and uplifting the brittle upper crust was rapidly uplifted and shortened by the shallow major thrusts which were developed on the d1 the d1 and d2 controlled the uplifting and shortening in the southeastern margin of the tibetan plateau the lower crust lc may be decoupled from the d2 and subducted due to the resistance by the stable craton underlying the sb the structural model manifests the importance of multi detachments and the superimposed deformation in the lms thrust belt however we emphasize that this crustal scale tectonic wedging only discovered in the central lms the tectonic wedge is an important uplifting pattern that should be not neglected

progress in deep lithospheric exploration of the continental china a review of the sinoprobe abstract the sinoprobe deep exploration in china is a multidisciplinary earth science research program that aims at revealing the composition structure and evolution of the continental lithosphere in china the sinoprobe 2008 2012 has successfully conducted research and field experiments on determining the crustal and mantle structures using new deep seismic and magnetotelluric mt exploration this has allowed the accumulation of new exciting data that have significantly accelerated china s development on deep lithospheric exploration the new data also led to new understandings on the mesozoic and cenozoic geological evolution of the continental china the main results of the sinoprobe so far include 1 a collection of ca 6000 km long seismic reflection profile data 2 a nation wide geochemical baseline 3 a nation wide 4 4 mt array and regional 1 1 mt arrays in the north china and the qinghai tibet plateau 4 three dimensional 3 d exploration of ore districts in the eastern china 5 several continental scientific drilling holes 6 regional in situ stress monitoring networks 7 geodynamic modeling of the lithosphere underneath the continental china and 8 instrumentation development for deep exploration in china etc for the first time the sinoprobe has obtained deep seismic reflection evidence for the moho surface below the thick crust of the central qinghai tibet plateau it also reveals dipping fabrics in the lithospheric mantle beneath the northeastern china the preliminary results from mt array observation of the sinoprobe show an abnormal electric conductivity structure of the lithosphere beneath the ordos basin providing important evidence for the evolution mechanism of the north china craton ncc generally the sinoprobe has conducted successfully during its initial phase 2008 2012 which has settled a foundation for the next phase of the sinoprobe in the future

late structural control of mesothermal vein hosted gold deposits in central victoria australia mineralization mechanisms and exploration potential abstract comparison of the structural relationships between five gold deposits in ordovician rocks of the central victorian slate belt reveals a similar history and structural control of gold mineralization large quartz veins spatially associated with gold mineralization such as the famous saddle reefs of bendigo formed during the second deformation earlier than the gold mineralization itself where they were overprinted by the effects of the fourth deformation they provided structural sites for gold deposition on their boundaries with country rock where brecciation jostling and fracture were favoured access of fluids resulting from metamorphism and deformation to the brecciated fractured and jostled blocks of country rock created conditions suitable for the precipitation of gold through a sequence of alteration replacement and infill the dominant structural relationships that resulted in the generation of these sites were a the high angle of the axial plane of the fourth deformation to earlier structures and b the presence during mineralization of large pre existing quartz veins that acted as structural discontinuities on which brecciation could occur these factors allow a predictive capacity for exploration in the region

orogenic gold common or evolving fluid and metal sources through time abstract orogenic gold deposits of all ages from paleoarchean to tertiary show consistency in chemical composition they are the products of aqueous carbonic fluids with typically 5 20 mol co 2 although unmixing during extreme pressure fluctuation can lead to entrapment of much more co 2 rich fluid inclusions in some cases ore fluids are typically characterized by significant concentrations of ch 4 and or n 2 common estimates of 0 01 0 36 mol h 2 s a near neutral ph of 5 5 and salinities of 3 7 wt nacl equiv with na k ca mg this fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation nevertheless there are broad ranges in more robust fluid inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths much of the reported isotopic and noble gas data is inconsistent between deposits leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces fluid stable isotope values are commonly characterized by the following ranges 1 18 o for precambrian ores of 6 to 11 and for phanerozoic ores of 7 to 13 2 d and 34 s values that are extremely variable 3 13 c values that range from 11 to 2 and 4 15 n of 10 to 24 for the neoarchean 6 5 to 12 for the paleoproterozoic and 1 5 to 10 for the phanerozoic secular variations in large scale earth processes appear to best explain some of the broad ranges in the o s and n data fluid rock interaction particularly in ore trap areas may cause important local shifts in the o s and c ratios the extreme variations in d mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion generations many which are not related to ore formation radiogenic isotopes such as those of pb sr nd sm and os measured on hydrothermal minerals are even more difficult to interpret for defining metal source particularly as the low salinity ore fluids transport limited amounts of these elements and significant amounts of these may be locally added to the minerals during alteration reactions at the sites of gold deposition noble gas and halogen data are equally equivocal fluid exsolution from granitoids emplaced into the upper and middle crust metamorphism of the crust or fluids entering trans crustal fault zones from below the crust all remain as permissive scenarios associated with orogenic gold formation as the abundant geochemical data are equivocal however geological and geochronological data weigh heavily against a magmatic hydrothermal model in the upper to middle crust there is no universal temporal association between orogenic gold and magmatism and where there is an overlap in age there is no specific type of magmatism consistently associated with gold formation nor element zonation around any specific pluton a crustal metamorphic model for fluid and metal sources is very consistent with geological geochronological and geochemical data although metamorphism on a regional scale that releases these components into major fault zones can be associated with many processes along active continental margins these can include crustal thickening and radiogenic heating slab rollback and heating during crustal extension or subduction of a spreading ridge heating the base of an accretionary prism in rare examples where phanerozoic orogenic gold deposits are hosted in precambrian high grade metamorphic terranes fluids and metals must however enter a transcrustal fault system from a sub crustal source this could either be a devolatilized subducted relatively flat perhaps stalled slab and its overlying sediment or the corner of the fertilized mantle wedge that releases a fluid during a thermal event

isostatic gravity anomaly lithospheric scale density structure of the northern tibetan plateau and geodynamic causes for potassic lava eruption in neogene abstract this paper will help to further constrain geodynamic models for the evolution of northern tibet through two techniques that employ bouguer gravity anomaly data the first is isostatic correction of bouguer gravity anomalies and the second is 2 d density modeling along a profile at 88 5 e from 30 n to 37 n within the tibetan plateau areas dominated by volcanic rocks exhibit ultra low bouguer gravity anomalies and low isostatic residual anomalies the 2 d density structure beneath profile 88 5 e shows a giant upward dome distributed body of low density in the middle lower crust and mantle beneath the high to ultra potassic areas suggesting that the original middle and lower crusts were reformed and replaced extensively in the area based on existing regional geology and tectonics geochemical data from magmatic rocks and geophysical information this paper proposes that the sustained northward subduction of the indian plate has resulted in breaking off of the frontal margin of the asian lithospheric mantle subsequently the original lithosphere was reactivated by thermal tectonic changes high to ultra potassic volcanoes erupted extensively in the northern tibetan plateau during neogene and the plateau experienced rapid ne trending uplift

relationships between gold concentration and structure in quartz veins from the hodgkinson province northeastern australia the hodgkinson province is a tract of multiply deformed silurian devonian rocks in north queensland australia gold bearing quartz veins from the west normanby goldfield in the northern hodgkinson province were emplaced during the permian d4 event broadly coeval with regional granite emplacement taylors fault a major structure that formed during d2 hosts the veins which infill dilatational jogs opened during sinistral normal reactivation of the fault in d4 veins contain graphitic laminations that formed when fault planes segmented wallrocks adjacent to the veins producing tabular clasts that were tectonically sliced into the reefs laminations are the result of progressive shear strain associated with continued movement on the faults which caused strain enhanced dissolution of silicate minerals and residual graphite enrichment in the clasts this process produced graphite coated shear planes that delimit zones of grain size reduction in the veins laminations commonly contain stylolites which nucleated on pronounced sinuosities of the shear planes due to progressive shortening during d4 gold particles have preferentially nucleated in zones of relatively coarser grained quartz adjacent to the shear planes where shortening strain caused microfracturing and allowed fluid access gold may have been introduced with the quartz but was redistributed within the reefs and localized along the laminations by the effects of synchronous progressive deformation regionally gold deposits show close spatial relationships with granite plutons of the permian whypalla supersuite relationships in the west normanby gold field support a regional model of reef emplacement and gold mineralization during the permian d4 event