dynamic modeling of slow slip coupled with tremor 1 we theoretically study the generation mechanism of slow slip in a dynamical framework assuming a fault in a fluid saturated thermoporoelastic medium the fluid flow is taken into consideration dynamic slip is assumed to create pores and cause shear heating on the fault key parameters in the modeling are su and su the nondimensional parameter su represents the relative dominance of the effect of pore creation on the fluid pressure change over that of shear heating while su is associated with the dominance of fluid flow effect over the effect of shear heating our calculation shows that we have to assume su 1 and relatively small values for su to simulate rupture speed that is negligibly small compared to the shear wave velocity although this was also found in our former paper our new finding here is the simulation of slow slip coupled with tremor we find that frozen slip is reactivated sporadically because the fluid inflow triggered by the pore creation elevates the fluid pressure on the fault the slip reactivation actually occurs if su is smaller than a threshold such sporadic reactivation of slips can be a model for slow slip coupled with tremor we also show that the moment evolution curves are categorized into two separate groups when su 0 1 one of them represents slow slips while the other represents ordinary earthquakes

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

interplate coupling in the kanto district central japan and the boso peninsula silent earthquake in may 1996 i studied crustal deformation in the kanto district central japan based on continuous gps data horizontal as well as vertical displacement rate demonstrate significant interaction between the landward kanto block and the philippine sea plate although the subduction effect of the pacific plate is not apparent it is reasonable to consider the entire kanto district is displaced westward due to the interaction with the pacific plate the gps velocity data were inverted to estimate the slip deficit distribution on the sagami trough subduction zone the result delineates a strongly coupled region on the plate interface part of which corresponds to the 1923 kanto earthquake the strongly coupled region is located shallower than 20 km in addition the plate interaction is laterally heterogeneous even in the same depth range implying thermal structure is not the only factor controlling interplate coupling the gps data also detected a silent earthquake event on the interface of the philippine sea slab east of the boso peninsula in the middle of may 1996 the silent rupture propagated over a 50 km 50 km wide area during about a week the maximum slip was approximately 50 mm and the released seismic moment was 4 7 1018nm mw 6 4 there was a small seismicity triggered by this silent event the silent slip was located in the peripheral of the strongly coupled area suggesting that frictional properties and or stress conditions are inhomogeneous on the plate boundary interface

oxygen isotope study of the kamioka zn pb skarn deposits central japan the kamioka zn pb deposits consist of clinopyroxene rich skarns replacing limestone lenses in hida gneissose rocks paleozoic metabasite early jurassic funatsu granitic rocks and late cretaceous porphyritic dikes and stocks are the known igneous rocks in the mining area oxygen isotopic compositions of eight separates each of clinopyroxene and quartz from the deposits table 1 and some minerals and rocks from the major rock units around the deposits table 2 have been analyzed the estimated oxygen isotopic ratios of the fluids responsible for the formation of the deposits range as low as 4 to 3 smow these values are considerably lower than expected from magmatic waters and demonstrate that none of the igneous rocks in the area could be a direct source of the skarn and ore forming fluids the data instead show that the deposits are formed by a huge convective circulation of solutions of meteoric water origin promoted by a hidden batholithic intrusion at the time of the late cretaceous

a slow thrust slip event following the two 1996 hyuganada earthquakes beneath the bungo channel southwest japan we report a slow thrust slip event that occurred beneath the bungo channel region southwestern japan on oct and dec 1996 two hyuganada earthquakes both mw 6 7 followed by afterslips occurred in addition a crustal movement characterized by an extremely slow rise was observed around the bungo channel about 200 km north from the epicenters and continued for about 300 days long assuming a slow slip on the plate boundary we estimate its duration and surface displacements from gps time series data by curve fitting and then determine the fault slip distribution we found that a slow slip without any earthquakes continued for nearly one year and released the seismic moment comparable to that of the hyuganada earthquakes occurrence of the slow thrust slip event suggests that this kind of event may be a characteristic mode of stress release at a transition region of interplate coupling

formation epoch and genesis of intrusive rocks in huogeqi orefield of inner mongolia and their relationship with copper mineralization ingle zircon mc icp ms u pb dating and lithogeochemical studies of gabbro diorite intrusives in the huogeqi orefileld were conducted for the purpose of constraining their petrogenesis and their relationship with copper mineralization zircons collected from gabbro diorite display oscillatory zoning and high th u ratios 0 20 0 77 indicating their magmatic origin a weighted average u pb age of 273 9 1 2 ma for huogeqi intrusive rocks was obtained suggesting that the formation of gabbro diorite should be associated with the collisional event of the north china plate and siberia plate in late hercynian period their initial hf isotope ratios and hf two stage depleted mantle model ages range from 4 1 to 10 0 and from 1 56 to 1 92 ga respectively their peak model ages are consistent with the bulk rock nd two stage depleted mantle model age of 1 77ga implying that the rock forming materials were mostly derived from the paleo crust instead of from the depleted mantle geological and geochemical characteristics of the gabbro diorite intrusives reveal that they were derived from partial melting of archaean basement and interacted with mantle derive magmas by about 17 as estimated by simulated calculation a comparison of geochemical characteristics between gabbro diorite intrusives and the copper ore body suggests that hercynian diorite failed to provide significant metallogenic elements furthermore hercynian diorite intruded in the compressive orogenic environment 273 9 ma ago whereas copper mi neralization occurred in middle late proterozoic suggesting the absence of direct genetic relationship between the plutonic intrusion and the formation of the copper ore body based on field observation and decrepitation curves of quartz and chalcopyrite the authors have reached the conclusion that the huogeqi copper deposit was reformed by magmatic hydrothermal fluid along the contact zone between the gabbro diorite and the copper ore body

p t x conditions origin and evolution of cu bearing fluids of the shear zone hosted huogeqi cu pb zn fe deposit northern china abstract huogeqi is a shear zone hosted epigenetic deposit within the greenschist amphibolite facies of the mesoproterozoic langshan group in the langshan district on the northern margin of the north china craton ncc copper mineralization in the huogeqi deposit was formed in two stages a main stage controlled by the shear zone and characterized by brittle ductile ore forming structures and a lower greenschist facies mineral assemblage and a late stage characterized by open space filling textures and low temperature minerals based on microthermometric and raman microprobe analysis the main stage cu bearing fluid was mesothermal low salinity and h 2 o ch 4 dominant and was generated by an interaction between a deep crustal metamorphic fluid and graphite bearing host rocks this interaction resulted in a more ch 4 rich fluid which was more amenable to be immiscible we showed that immiscibility of the h 2 o ch 4 fluid occurred due to temperature decrease prior to the main stage cu mineralization cu was finally precipitated from the resultant h 2 o rich aqueous fluid main stage cu mineralization temperature was obtained using various methods 310 370 c by intersection of isochors of coexistent ch 4 and aqueous inclusions 364 41 c on average by pressure correction of the homogenization temperatures of aqueous inclusions and 362 26 c using the chlorite geothermometer pressure during cu deposition fluctuated between lithostatic and hydrostatic at depths of ca 10 12 km but it seemingly had no effect on the mineralization process the late stage cu bearing fluid was a low temperature low salinity h 2 o of meteoric origin

detection and monitoring of ongoing aseismic slip in the tokai region central japan analysis of global positioning system data shows that the rate of crustal deformations in the tokai region of japan a seismic gap area changed over the past 18 months kalman filtering analysis shows aseismic slip on the plate boundary in the western tokai region centered on lake hamana adjacent to the anticipated tokai earthquake source area the cumulative moment magnitude reaches 6 7 in june 2002 with a relative slip increase northeast of lake haman from january 2002 an existence of aseismic slip in the western tokai supports the hypothesis of a silent event as the cause of uplifting several days before the 1944 tonankai earthquake

geology fluid inclusion geochemistry and 40ar 39ar geochronology of the wulasigou cu deposit and their implications for ore genesis altay xinjiang china abstract the wulasigou cu deposit occurs as veins controlled by a nw trending structure in a devonian volcano sedimentary basin of the altay orogenic belt xinjiang china igneous and sedimentary rocks exposed in the area have undergone greenschist facies metamorphism the ore forming process can be divided into early middle and late stages represented by respectively pyrite quartz polymetallic sulfide quartz and carbonate quartz veins veinlets and or replacement bodies the early veins were deformed and brecciated during a compressional or transpressional event the middle stage veinlets filled fractures in the early stage vein and alteration assemblages and are undeformed suggesting a tensional shear setting the late stage veinlets are mainly open space fissure fillings that cut veins and replacement bodies formed in the earlier stages four types of fluid inclusions fis including aqueous w type mixed carbonic aqueous m type purely carbonic c type and daughter mineral bearing s type have been identified in copper related quartz and calcite from the wulasigou deposit the early stage quartz contains m and w type primary fis that completely homogenized at temperatures of 322 412 c with low salinities of 0 9 6 5 wt nacl equiv in contrast the late stage quartz or calcite contains only the w type fis with homogenization temperatures of 101 234 c and salinities of 0 9 2 9 wt nacl equiv this indicates that the metallogenic system evolved from co 2 rich metamorphic to co 2 poor through input of meteoric fluids all four types of fis can only be observed in the middle stage minerals where they show evidence of vein formation during an episode of fluid immiscibility these fis homogenized at temperatures ranging mainly from 230 to 347 c with salinities clustering 2 7 10 2 wt nacl equiv for the w m and c types and 34 7 38 2 wt nacl equiv for the s type respectively the metal precipitation resulted from a decrease in copper solubility during the fluid immiscibility episode the estimated trapping pressures for the middle stage fluids are 1 55 3 55 kbar suggesting an alternating lithostatic hydrostatic fluid system controlled by fault valve activity at a depth of 13 15 5 km muscovite separates from the middle stage polymetallic quartz veinlets yield a well defined 40 ar 39 ar isotopic plateau age of 219 41 2 10 ma and an 39 ar 36 ar 40 ar 36 ar isochron age of 219 73 2 17 ma this age postdates the final paleo asia ocean closure at ca 250 ma by about 30 ma and indicates that the cu mineralization at wulasigou has occurred in the triassic continental collision setting hence the wulasigou cu deposit may be the first example of orogenic lode cu deposits formed in accretionary orogeny or continental collision

short term slow slip and correlated tremor episodes in the tokai region central japan 1 we observe the related phenomenon of short term slow slip event sse and low frequency nonvolcanic tremor on the deeper extension of the 1944 tonankai and the anticipated tokai earthquake rupture areas central japan japan nation wide seismometer and tiltmeter array nied hi net has recorded these correlated episodes of sse and tremor known as episodic tremor and slip ets in 2004 and 2005 the events are located on two areas in the tokai region one is near the shima peninsula and the other is around the aichi area both episodes have a typical duration of 2 3 days and released seismic moment corresponding to mw 6 0 moreover these episodes repeatedly occur with a recurrence interval of about six months in both areas this evidence suggests that the coincidence between the sse and the tremor is a characteristic behavior in the whole tremor belt like zone in the nankai trough subduction zone

the frequency size scaling of non volcanic tremors beneath the san andreas fault at parkfield possible implications for seismic energy release abstract we analyse the frequency size distribution of non volcanic tremors observed along the parkfield section of the san andreas fault we suggest that these non volcanic tremors follow a power law scaling typical of scale invariant stick slip tectonic earthquakes but with an unusually high scaling exponent of more than 2 0 and a systematic depth dependency while each individual non volcanic tremor releases only a minuscule amount of energy and slip this is more than compensated by their sheer numbers consequently the integrated contribution of this largely invisible seismicity non volcanic tremors and nano earthquakes is non negligible and could potentially account in selected patches along the san andreas fault for up to 100 of the plate motion

a group of rifting events in the terminal paleoproterozoic in the north china craton abstract rifting events of the terminal paleoproterozoic are well preserved in the north china craton they include an aulacogen and cratonic marginal rift basins mafic dyke swarms two anorthosite suites and rapakivi granites all of these events took place after metamorphism deformation and magmatism of the late paleoproterozoic between 2 0 ga and 1 85 ga or 1 80 ga the rifting events belong to an anorogenic event group reflecting breakup of a late paleoproterozoic united north china craton an intracratonic rift basin in the center of the north china craton is named the yanshan taihangshan aulacogen a stratigraphic thickness of 9193 m was deposited within the basin including three groups and twelve formations with time range ca 1 8 ga to 0 85 ga the oldest changcheng group of the sequence was deposited in a graben and is mainly composed of alluvial basal conglomerates terrestrial clastic rocks and shallow marine sandstone and carbonates with super high potassium basalt trachyte the marginal basins occur around the northern western and southern margins of the north china craton respectively located in langshan baiyun obo helanshan mountain and the adjacent regions between henan shanxi and shaanxi provinces the stratigraphic sequences of the basins are generally made up of clastic rocks in the lower parts and carbonates in the upper part with a thick volcanic sequence with u pb age of 1840 14 ma exposed in the southern marginal regions based on stratigraphic sequences isotopic data and volcanic features the initial rifts took place at about 1 85 ga to 1 80 ga mafic dyke swarms are largely developed in central parts of the north china craton where they intrude archean granulite and high amphibolite rocks a new single zircon u pb isotopic age of 1769 2 5 ma has been reported from a mafic dyke in east henshan mountain northwestern shanxi province an anorthosite suite agms is exposed along two deep fault belts in northern hebei province isochron ages of 1683 193 ma by rb sr and 1735 239 ma by sm nd were measured from an anorthosite body the rapakivi granites crop out along the miyun qiangzilu xinglong fault in an e w direction and are characterized by megacrysts of alkali feldspars mantled by plagioclase thus showing many of the petrographic features of classic rapakivi granites worldwide a typical rapakivi body preserved in shachang of miyun county beijing has a u pb age of 1716 31 ma super high potassium volcanics located in the upper changcheng group have been dated at 1683 67 ma and 1625 6 ma the time range for all magmatic events is between 1 72 ga and 1 62 ga

isotope geochemistry of the tieluping silver lead deposit henan china a case study of orogenic silver dominated deposits and related tectonic setting the tieluping silver deposit which is sited along ne trending faults within the high grade metamorphic basement of the xiong er terrane in the qinling orogenic belt is part of an important recently discovered mesozoic orogenic type ag pb belt ore formation includes three stages an early barren quartz pyrite stage e an intermediate polymetallic sulfide ore stage m and a late barren carbonate stage l carbon sulfur and lead isotope systematics indicate that the e stage fluids are deeply sourced the l stage fluids are shallow sourced meteoric water whereas the m stage fluids are a mix of deep sourced and shallow sourced fluids sulfur and lead isotope data show that the ore forming fluids must have originated from a source with elevated radiogenic lead and low 34s values that differs significantly from exposed geologic units in the xiong er terrane the lower crust and the mantle this supports the view that the carbonate shale chert sequences of the guandaokou and luanchuan groups south of the machaoying fault might be the favorable sources although little is known about their isotopic compositions a tectonic model that combines collisional orogeny metallogeny and hydrothermal fluid flow is proposed to explain the formation of the tieluping silver deposit during the mesozoic collision between the north china craton and south china block early mid triassic indosinian orogeny crustal slabs containing the carbonate shale chert sequences of the guandaokou and luanchuan groups locally rich in organic matter carbonaceous shale were thrust northwards beneath the xiong er terrane along the machaoying fault metamorphic devolatilisation of this underthrust slab probably provided the ore forming fluids to develop the ag pb ore belt which includes the tieluping silver deposit fluids and magmas were emplaced during extensional stages related to the jurassic cretaceous yanshanian orogeny

integration of transient strain events with models of plate coupling and areas of great earthquakes in southwest japan we model the crustal deformation caused by two long term subduction slip transients in southwest japan which we refer to as the 2000 2004 tokai and the 2002 2004 bungo channel slow slip events sses we use re analysed geonet position time series and a kalman filter based network inversion method to image the spatiotemporal slip variation of the two events on the plate interface during the period of 1998 2004 67 and 2000 2005 both events are found to have complex slip histories with multiple subevents in addition to a newly identified slip subevent in 2002 2003 we find that the major event in the bungo channel sse initiated in early 2003 beneath the northeastern corner of the region and expanded southwestward in contrast to the slip characteristics suggested by other studies the re analysed gps data in the tokai region shows a renewed slip activity for the tokai sse in early 2003 2004 at a similar location as in the period of 2001 2002 the equivalent m w for both the tokai and bungo channel sses are about 7 0 our results show that the tokai sse appears to start before the miyaki kozu seismovolcanic event integrating plate coupling and sses shows that the transient slip zones are located in a region between the locked zones and the epicentres of the low frequency earthquakes lfes at least part of the interseismic slip deficit is released by episodic sses beneath the bungo channel region we find excellent temporal correspondence between transient slip and adjacent lfes for both sse suggesting that they are closely related and possibly reflect that long term slow slip may modulate the occurrence of lfes

synchronous changes in the seismicity rate and ocean bottom hydrostatic pressures along the nankai trough a possible slow slip event detected by the dense oceanfloor network system for earthquakes and tsunamis donet abstract we detected long term hydrostatic pressure changes at ocean bottom stations of the dense oceanfloor network system for earthquakes and tsunamis donet along the nankai trough off southwestern japan we detected these changes after removing the contributions of ocean mass variations and sensor drift from the records in addition we detected a decrease in the background seismicity rate of a nearby earthquake cluster that was synchronous with the hydrostatic pressure changes we interpreted these observed hydrostatic pressure changes to reflect vertical deformation of the ocean floor of 3 8 cm and we consider the cause of the seafloor crustal deformation to be a slow slip event sse beneath the stations because the pressure changes were observed at stations with distances less than 20 km to each other we inferred that the sse occurred in the shallow part of the sedimentary wedge such as on a splay fault system the synchronous observation of an sse and a seismicity rate change suggests that both were triggered by a change in the regional stress that may be associated with stress accumulation and release processes occurring along the nankai trough these data show that continuous and careful monitoring of crustal activities by donet stations provides an effective way to detect seismic and geodetic signals related to the occurrence of megathrust or other types of large earthquakes

ore forming conditions and genesis of the huogeqi cu pb zn fe deposit in the northern margin of the north china craton evidence from ore petrologic characteristics abstract the huogeqi cu pb zn fe deposit is located in the langshan district in the western segment of the northern margin of the north china craton the deposit is hosted by upper greenschist lower amphibolite facies 550 650 c rocks of the langshan group most orebodies are hosted in a shear zone that developed in parallel with the sedimentary bedding of the langshan group fe was precipitated coeval with the deposition of the host rocks i e a syngenetic origin whereas cu pb and zn were precipitated in hydrothermal systems postdating formation of the host rocks i e an epigenetic origin the hydrothermal mineralization process can be subdivided into two stages 1 a main stage with predominant cu pb zn mineralization stage where ore forming structures are characterized by brittle ductile and brittle shear deformation the main stage sulfide veins cut the mylonite fabrics of the host rocks mineral paragenesis and compositions indicate that main stage cu mineralization took place at 330 440 c and 3 4 3 9 kbar this pressure temperature p t condition is consistent with that of the brittle ductile transition zone but lower than that of the peak metamorphism of the host rocks compared with cu mineralization the main stage pb zn mineralization took place at relatively lower temperature and pressure the syngenetically formed fe orebodies and iron formations in the huogeqi deposit were favorable sites for epigenetic cu precipitation the h 2 s rich cu fluids would have reacted with fe in the host rocks when flowing through fe orebodies and iron formations such a reaction would have led to a reduction in h 2 s of the ore forming fluids and consequently cu precipitation 2 the late stage cu mineralization is of less economic importance characterized by open space filling textures and a low temperature mineral assemblage that constrains the ore forming temperature as lower than 330 c this late stage mineralization took place in an epithermal like hydrothermal system at a shallower crustal depth

dynamic deformation of the accretionary prism excites very low frequency earthquakes 1 we have detected anomalous very low frequency earthquakes within the accretionary prism along the nankai trough southwestern japan centroid moment tensor inversion analysis reveals that the earthquake hypocenters are distributed at 10 km depth above the upper surface of the subducting philippine sea plate and within 50 70 km landward of the trough axis the focal mechanisms indicate reverse faulting their hypocenters are distributed beneath a deformation zone of an accretionary prism in sea floor topography these observations suggest that the occurrence of very low frequency earthquakes is related to numerous reverse fault systems within the accretionary prism and that the earthquakes reflect the dynamics of deformation within this accretionary prism

tracing the ore formation history of the shear zone controlled huogeqi cu pb zn deposit in inner mongolia northern china using h o s and fe isotopes abstract the original ore fluid of the huogeqi cu pb zn deposit in inner mongolia northern china was enriched in heavy oxygen isotopes with 18o values ranging from 9 9 to 11 4 per mil which is characteristic of the metamorphic devolatilization of pelitic rocks the d values determined by direct measurement of syn ore hydrothermal tremolite range from 116 to 82 per mil lying between the domains of typical metamorphic fluid and meteoric water which is in equilibrium with organic matter oxygen and hydrogen isotope ratios indicate that the ore fluid was derived from deep sourced metamorphic fluid and interacted with organic rich shale during fluid migration which is consistent with the fluid evolution history revealed by a previous fluid inclusion study sulfides in the deposit are characteristically enriched in heavy s isotopes with an average 34s value of 13 4 6 2 per mil 1 n 103 the s isotope ratios are identical to stratabound sulfides generated through the non bacterial reduction of neoproterozoic marine sulfate with 34s values of 17 per mil previous studies on lead isotopes of sulfides revealed that the ore forming metals cu pb and zn at the huogeqi deposit were also remobilized from a stratabound source this source was syngenetically elevated in its cu pb and zn sulfide content as a result of submarine hydrothermal activities forming sulfide rich layers within a rift tectonic setting the fe isotope ratios for sulfides are consistent with those of an intercalated iron formation within the ore hosting rocks suggesting that the fe in the sulfides was derived from local host rocks during sulfide precipitation and the fe rich rocks are favorable lithological units for high grade mineralization the heterogeneous sources of ore fluid s ore forming metals and fe are explained by a multistage genetic model which is supported by the geological characteristic of the deposit the enriched sulfides were subsequently remobilized and enriched by metamorphic devolatilization during the permian and triassic periods the metamorphic ore fluid ascended along a shear zone and interacted with organic rich shale sulfides eventually precipitated within the shear zone at a shallower crustal level especially where the shear zone intersected fe rich host rocks this multistage genetic model has implications for mineral exploration greenschist to amphibolite facies terranes containing thick neoproterozoic rift sequences are ideal regions for potential cu pb zn mineralization in particular intercalated volcanic rocks within the rift sequences are indicative of high heat flow and are ideal for the development of submarine hydrothermal systems the primary structures hosting mineralization and ore shoots in the huogeqi area are jogs in the shear zones in addition fe rich lithological units such as iron formations are ideal hosts for high grade ore

contrasting late carboniferous and late permian middle triassic intrusive suites from the northern margin of the north china craton geochronology petrogenesis and tectonic implications two contrasting intrusive suites have been identified from the northern margin of the north china craton a late carboniferous dioritegranodiorite suite mainly made up of quartz diorite diorite granodiorite tonalite and hornblende gabbro and a late permian middle triassic suite of granitoid intrusions consisting of monzogranite syenogranite and quartz monzonite plutons from the late carboniferous suite exhibit variable sio2 contents and calc alkaline or high k calc alkaline metaluminous geochemical features most have low negative whole rock nd t values where t is the crystallization age of 17 1 to 11 5 and zircon hf t values of 38 3 to 11 2 indicating that they were derived mainly from anatectic melting of the ancient lower crust with some involvement of mantle materials however an older pluton in the suite exhibits higher nd t values of 11 5 to 9 9 nd model ages of 1 82 1 64 ga lower initial 87sr 86sr ratios of 0 7046 0 7048 and it contains some zircon grains that are characterized by high negative to positive zircon hf t values of 8 7 to 1 2 indicating strong involvement of juvenile materials derived from the lithospheric mantle the late carboniferous plutons are interpreted as subduction related and to have been emplaced in an andean style continental margin arc during the southward subduction of the paleo asian oceanic plate beneath the north china craton rocks from the late permian middle triassic intrusive suite display geochemical signatures ranging from highly fractionated i type to a type they exhibit higher zircon hf t values of 14 9 to 6 7 whole rock nd t values of 10 6 to 8 8 and younger hf and nd model ages than most of the late carboniferous plutons indicating that they could have been produced by extreme fractional crystallization of hybrid magmas resulted from mixing of coeval mantle and crust derived melts they are interpreted as postcollisional postorogenic granitoids linked to lithospheric extension and asthenosphere upwelling due to slab break off and subsequent sinking after final collision and suturing of the mongolian arc terranes with the north china craton these two contrasting intrusive suites suggest that the final closure of the paleo asian ocean and collision between the mongolian arc terranes and the north china craton occurred during the late permian and these events were followed by postcollisional postorogenic extension large volume magmatism and significant continental growth no significant syncollisional crustal thickening high pressure metamorphism or s type granitoid magmatism occurred during the collision process

the effects of weathering variability and anthropogenic pressures upon silicon cycling in an intertropical watershed tana river kenya abstract we present the first study of the si isotopic composition of dry season river waters from the tana river kenya data encompasses the entire river basin with samples collected from headwaters to the estuary thereby capturing a salinity gradient in the headwaters the isotopic signature is affected by climate as a result of its control on soil drainage and weathering the 30 si signatures in the basin range from 0 69 up to 2 23 signatures are clearly affected by dams an increase in 30 si ratios of 0 54 and a decrease in the dissolved si dsi concentration by 41 were observed downstream of the masinga dam the largest of a succession of 5 hydroelectric dams this reduction in si load is most likely due to increased diatom productivity as the corresponding change in 30 si signature is consistent with the known fractionation by these organisms the 30 si composition of waters entering the estuary is ca 2 and dsi concentrations are 349 m in the estuary the dsi concentrations decrease linearly following the salinity while the 30 si ratio remains stable indicating the absence of processes affecting the dsi pool for the studied range of salinity

genesis of the dadonggou pb zn deposit in kelan basin altay nw china constraints from zircon u pb and biotite 40ar 39ar geochronological data abstract the genesis of polymetallic deposits in southern altay nw china has been disputed between a syngenetic seafloor hydrothermal process and an epigenetic orogenic type mineralization the dadonggou pb zn deposit occurs as nw trending veins in the devonian kangbutiebao formation volcanic sedimentary sequence in the kelan basin southern altay a set of integrated zircon u pb and biotite 40ar 39ar geochronological data were applied to constrain the forming ages of the ores and their country rocks three samples of host volcanic rocks yielded weighted mean 206pb 238u ages of 397 1 4 5 ma 391 7 3 6 ma and 391 1 4 2 ma respectively indicating that the kangbutiebao formation was deposited in a devonian back arc basin two biotite samples separated from the pb zn containing quartz veins yielded 40ar 39ar plateau ages of 205 9 2 1 ma and 204 3 2 2 ma respectively which represent the age of the pb zn mineralization that is attributed to the closure of the kelan back arc basin and the late triassic orogeny combining the available geological and geochronological data this contribution outlines the successive evolution from the development of a devonian back arc basin to the late triassic post subduction orogeny and proposes that the dadonggou pb zn deposit is an epigenetic orogenic type deposit placed in the late triassic orogeny

spatial evolution of zn fe pb isotopes of sphalerite within a single ore body a case study from the dongshengmiao ore deposit inner mongolia china analyses of sphalerite minerals from the characteristic brecciated zn pb ores of the main ore body in the giant dongshengmiao deposit have revealed variations in 66zn from 0 17 to 0 40 and in 56fe from 1 78 to 0 35 further the investigated pyrrhotite samples have iron that is isotopically similar to that of associated sphalerite minerals the most distinctive pattern revealed by the zinc and iron isotope data is the lateral trend of increasing 66zn and 56fe values from southwest to northeast within the main ore body the lead isotopic homogeneity of ore sulfides from the main ore body suggests that there is only one significant source for metal thus precluding the mixing of multiple metal sources as the key factor controlling spatial variations of zinc and iron isotopes the most likely control on spatial variations is rayleigh fractionation during hydrothermal fluid flow with lighter zn and fe isotopes preferentially incorporated into the earliest sulfides to precipitate from fluids precipitations of sphalerite and pyrrhotite have played vital roles in the zn and fe isotopic variations respectively of the ore forming system accordingly the larger isotopic variability for fe than zn within the same hydrothermal system perhaps resulted from a larger proportion of precipitation for pyrrhotite than for sphalerite the lateral trend pattern revealed by the zinc and iron isotope data is consistent with the occurrence of a cystic shaped breccia zone which is characterized by marked elevation in cu the results further confirm that zn and fe isotopes can be used as a vectoring tool for mineral prospecting

cratonic reactivation and orogeny an example from the northern margin of the north china craton abstract reactivation of cratonic basement involves a number of processes including extension compression and or lithospheric delamination the northern margin of the north china craton ncc adjacent to the inner mongolian orogenic belt was reactivated in the late paleozoic to early mesozoic during this period the northern margin of the ncc underwent magmatism n s compression regional exhumation and uplift including the formation of e w trending thick skinned and thin skinned south verging folds and south verging ductile shear zones zircon u pb shrimp ages for mylonite protoliths in shear zones which show ages of 310 290 ma mid carboniferous early permian constraining the earliest possible age of deformation muscovite within carbonate and quartz feldspar muscovite mylonites from the kangbao weichang and fengning longhua shear zones defines a stretching lineation and gives 40ar 39ar ages of 270 250 ma 250 230 ma 230 210 ma and 210 190 ma deformation developed progressively from north to south between the late paleozoic and triassic exhumation of lower crustal gneisses high pressure granulites and granites occurred at the cratonic margin during post ductile shearing 220 210 ma an undeformed early jurassic 190 180 ma conglomerate overlies the deformed rocks and provides an upper age limit for reactivation and orogenesis deformation was induced by convergence between the southern mongolia and north china cratonic blocks and the location of this convergent belt controlled later deformation in the yanshan tectonic province this province formed as older e w trending archean proterozoic sequences were reactivated along the northern margin of the ncc this reactivation has features typical of cratonic basement reactivation compression crustal thickening remelting of the mid to lower crust and subsequent orogenesis adjacent to the orogenic belt

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

geochronological and mineralogical constraints on mineralization of the hetai goldfield in guangdong province south china abstract the hetai goldfield located in the southern segment of the qinzhou bay hangzhou bay juncture orogenic belt qhjb is the largest concentration of gold deposits in guangdong province south china the gold mineralization is hosted within the late neoproterozoic to early paleozoic yunkai group and strictly confined to mylonite ductile shear zones the nature of the structural control of mineralization in particular the role of ductile versus brittle deformation and their ages which remain unclear despite numerous previous studies are examined in this paper through an integrated study of geochronology and mineralogy lamellar and filament structures shown by pyrite and pyrrhotite in the ores suggest that sulfidation took place during ductile deformation and syntectonic metamorphism but the majority of the ores are associated with brittle deformation features in combination with macroscopic and microscopy observations on shear fabrics la icp ms u pb dating on zircons of hydrothermal origin from mylonites suggests that the hetai goldfield was subjected to two shearing events an early sinistral ductile shearing at ca 240 ma and a late dextral ductile brittle shearing at ca 204 ma indosinian these ages are ca 90 30 ma older than the previously published gold mineralizing ages of ca 175 152 ma yanshanian suggesting that the main gold mineralization and related brittle deformation significantly postdate the ductile deformation this inference is supported by the mineralization temperatures estimated from geothermometers of arsenopyrite ca 350 290 c chlorite ca 260 230 c and sphalerite ca 230 170 c intergrown with native gold which are considerably lower than that for the ductile deformation 500 300 c or higher based on these data we propose that the gold mineralization in the hetai goldfield predominantly occurred during the yanshanian event and only minor gold mineralization and associated sulfidation took place during the earlier indosinian ductile deformation

fe isotope fractionation on fes formation in ambient aqueous solution iron sulfide phases are the ultimate repository of iron and reduced sulfur in sediments the sulfur isotope geochemistry of pyrite has had much to tell us about modern and ancient earth environments and it is likely that fe isotopes will too once fractionations for key processes are known we report the results of an experimental study of fe isotope fractionation on precipitation of fes synthetic mackinawite from excess aqueous fe ii solutions by addition of sodium sulfide solution at 2 40 c the results show a significant kinetic isotope effect in the absence of a redox process no detectable effect of temperature on the fractionation factor was observed the fe isotope fractionation for zero age fes is fe ii fes 0 85 0 30 across the temperature range studied giving a kinetic isotope fractionation factor of fe ii fes 1 0009 0 0003 on ageing the fes in contact with aqueous fe ii becomes progressively isotopically heavier indicating that the initial fractionations are kinetic rather than equilibrium from published reaction mechanisms the opportunity for fe isotope fractionation appears to occur during inner sphere ligand exchange between hexaqua fe ii and aqueous sulfide complexes fe isotope fractionation on mackinawite formation is expected to be most significant under early diagenetic situations where a readily available reactive fe source is available since fes aq is a key reactive component in natural pyrite formation kinetic fe isotope fractionations will contribute to the fe isotope signatures sequestered by pyrite subject to the relative rate of fes2 formation versus fes fe ii aq isotopic equilibration

evolution of the solonker suture zone constraints from zircon u pb ages hf isotopic ratios and whole rock nd sr isotope compositions of subduction and collision related magmas and forearc sediments abstract the solonker zone in northern inner mongolia china is considered as the suture between the north china craton and the south mongolian microcontinent two magmatic belts are recognized along the suture zone a subduction related magmatic belt represented by the baolidao arc rocks and a younger collision related granite belt represented by the halatu granites we use zircon u pb ages zircon in situ hf isotopic analyses and whole rock nd sr isotopic data of the two magmatic belts and related forearc sediments the xilinhot metamorphic complex to constrain timing of the suturing and to discuss the petrogenesis of the magmatic rocks a gabbroic diorite bld 1 of the baolidao arc was dated at 310 5 ma by shrimp this sample shows an e nd t value of 2 5 and i sr of 0 7052 hf isotopic analyses on 25 zircons from the same sample show e hf t 5 4 to 11 5 another diorite sample xh 2 of the same arc from south of xilinhot displays even more depleted isotopic compositions with e nd t 5 6 and i sr 0 7037 the main population of zircons from this sample have highly variable and depleted hf isotopic compositions e hf t 0 18 3 the large variation in hf isotopic composition of zircons with largely the same crystallization age from a single pluton is explained by a mixing process between depleted mantle derived magma and continental crust in an active continental arc setting the halatu granite hlt 2 was dated at 234 7 ma by shrimp zircons from the granite also show a large variation of e hf t values 9 1 to 26 despite most samples having whole rock e hf t 2 the large variation in e hf t values suggests that the granite formed probably by partial melting of two source regions a dominant juvenile crust and a subordinate old continental crust most zircons from the xilinhot metamorphic complex show ages comparable with those of the baolidao arc rocks suggesting that the protolith of the metamorphic complex was probably deposited during or after arc magmatism some zircons however show precambrian ages that fall into two groups one with ages of 780 900 ma resembling those from the south mongolian microcontinent and the other with ages of 1524 2900 ma similar to those of the north china craton thus the protolith of the metamorphic complex probably formed in a forearc basin during convergence of the two continents and metamorphosed subsequently during collision in the late paleozoic our zircon age data thus constrain timing of collision between the south mongolian microcontinent and the north china craton to have been between 296 and 234 ma

low frequency continuous tremor around the moho discontinuity away from volcanoes in the southwest japan 1 recent enhancement of seismic networks in the japan islands revealed occurrence of low frequency continuous tremors of a beltlike distribution in the southwest japan where the subducting philippine sea plate reaches depths of 30 40 km source depth of the tremor is estimated by selecting tremor segments with relatively clear p wave onsets the source region of the tremor is assumed to correspond to lowermost parts of crust close to a triple boundary of the crust mantle wedge and the subducting slab the long duration of the phenomenon indicates existence of fluid relating to the generation of the tremor the most probable fluid is considered to be water produced by dehydration process of chlorite and amphibole in the slab on the basis of data from high pressure and temperature experiments the northern border of the beltlike distribution is possibly rimmed by the edge of the mantle wedge because serpentine formation absorbs fluid water

geodynamic settings and tectonic model of skarn gold deposits in china an overview seventy skarn type gold deposits including 1 super large 19 large and 24 medium sized are known from different geotectonic units of china they contain a total resource of approximately 1000 t of gold 625 t in south china and account for 20 of china s gold reserves these skarn deposits are sited in collisional orogenic belts fault controlled magmatic belts and reactivated cratonic margins all of the chinese skarn gold provinces were affected by phanerozoic collisional orogenesis the timing of the metallogenic events and the spatial temporal distribution of the chinese skarn gold deposits indicates that they were formed during ore forming processes linked to the transition from shortening to extension in the geodynamic evolution of a collision orogen and not to subduction systems as is commonly advocated for porphyry copper systems around the pacific rim

iron isotope fractionation during skarn type metallogeny a case study of xinqiao cu s fe au deposit in the middle lower yangtze valley abstract fe isotope compositions of mineral separates and bulk samples from xinqiao cu s fe au skarn type deposit were investigated an overall variation in 57 fe values from 1 22 to 0 73 has been observed which shows some regularity the 57 fe values of endoskarn and the earliest formed fe mineral phase magnetite are ca 1 2 and ca 0 3 lower respectively relative to the quartz monzodiorite stock indicating that fluid exsolved from the stock is enriched in light fe isotopes moreover spatial and temporal variations in 57 fe values are observed which suggest iron isotope fractionation during fluid evolution precipitation of fe bearing minerals results in the fe isotope composition of residual fluids evolving with time precipitation of fe iii minerals incorporating heavy iron isotopes preferentially leaves the remaining fluid enriched in light isotopes while precipitation of fe ii minerals preferentially taking up light iron isotopes and makes the fe isotopic composition of the fluid progressively heavier the regularity of fe isotope variations occurred during fluid exsolution and evolution indicates that the dominant fe source of xinqiao deposit is magmatic overall this study demonstrates that fe isotope composition has great potential in unraveling ore forming processes as well as constraining the metal sources of ore deposits

metallogeny of the north china craton link with secular changes in the evolving earth abstract the north china craton ncc has experienced a complex geological evolution since the early precambrian and carries important records of secular changes in tectonics and metallogeny here we synthesize the salient geological and tectonic features of the evolution and destruction of the ncc vis a vis major metallogenic events and the formation of potential ore deposits we identify a close relationship between the major geological events in the ncc and those reported elsewhere on the globe we trace the records of a regular change in the pattern of metallogeny mineral deposit character spatial distribution and genetic mechanisms which closely match the timing and styles of the major geological and tectonic events in this craton the ncc went through five major tectonic cycles 1 neoarchean crustal growth and stabilization 2 paleoproterozoic rifting subduction accretion collision with imprints of the great oxidation event goe 3 late paleoproterozoic neoproterozoic multi stage rifting 4 paleozoic orogenesis at the margins of the craton and 5 mesozoic extensional tectonics associated with lithospheric thinning and decratonization coinciding with these major geological events are five major metallogenic systems identified as follows 1 an archean bif system 2 paleoproterozoic cu pb zn and mg b systems 3 a mesoproterozoic ree fe pb zn system 4 a paleozoic orogenic cu mo system and 5 mesozoic intracontinental au and ag pb zn and mo systems the ore deposit types in each of these metallogenic systems show distinct characteristics and tectonic affinities from early precambrian through late precambrian to paleozoic and mesozoic the ncc records a transition from primitive to modern style plate tectonics evidence for imbricated oceanic plate stratigraphy in a subduction accretion setting and collisional orogenesis along at least three major zones of ocean closure are documented major transitions in tectonic style and surface environmental changes recorded in other parts of the world are also reflected in the geological history and metallogenic events in the ncc large scale gold deposits formed through intraplate tectonics during the mesozoic provide important insights into mantle dynamics and crust mantle interaction associated with lithospheric thinning and craton destruction the ncc provides one of the best examples for documenting secular changes in the geological history and metallogenic epochs of an evolving earth

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

deep tremor in new zealand triggered by the 2010 mw8 8 chile earthquake 1 deep non volcanic tremor nvt is usually associated with episodic slow slip events new zealand is one notable exception where numerous slow slip events have been identified yet nvt has remained undetected here we present the first known case of triggered nvt at new zealand s hikurangi subduction margin following the mw8 8 chilean earthquake of february 27 2010 we identify coherent high frequency tremor signals that are in phase with and modulated by the passing rayleigh waves this is consistent with the surface wave triggering potential for strike normal incidence on a low angle thrust fault after constraining the tremor depth on the plate interface we locate the tremor source within 20 km of the source area of episodic slow slip the tremor location is also near the edge of a region with high seismic attenuation that marks the boundary between dehydrated subducted slab and inferred hydrated underplated sediment we speculate that reduced interface friction and high fluid pressures provided by fluid rich underplated sediment facilitates the tremor generation

ore geology and fluid inclusion geochemistry of the tiemurt pb zn cu deposit altay xinjiang china a case study of orogenic type pb zn systems abstract the tiemurt pb zn cu deposit is hosted in a devonian volcanic sedimentary basin of the altay orogenic belt and is thus interpreted to have formed by sea floor hydrothermal exhalation in previous studies our investigation discovered that the deposit is not stratiform or stratabound but structure controlled instead the hydrothermal ore forming process can be divided into the early middle and late stage represented by pyrite quartz polymetallic sulfide quartz and carbonate quartz veinlets respectively the early stage veins and contained minerals are structurally deformed and brecciated suggesting a compressional or transpressional tectonic regime the middle stage veinlets intrude and infill the fissures of the early stage assemblages and show no deformation suggesting a tensional shear setting the late stage veinlets mostly infill open space fissures that crosscut veins and replacements formed in the earlier stages four types of fluid inclusions fis including aqueous type w carbonic aqueous type c pure carbonic type pc and solid bearing type s are identified at the tiemurt deposit the early stage minerals contain the c and w type primary fis that are totally homogenized at temperatures of 330 390 c with low salinities of 0 8 11 9 wt nacl eqv whilst the late stage quartz or calcite contains only the w type fis with homogenization temperatures of 118 205 c and salinities of 1 4 3 4 wt nacl eqv this indicates that the ore fluid system evolved from co2 rich probably metamorphic to co2 poor meteoric fluids and that a significant co2 escape must have occurred all the four types of fis can be only observed in the middle stage minerals and even in a microscopic domain of a crystal representing an association trapped from a boiling fluid system these fis homogenize at temperatures ranging from 270 to 330 c with two salinity clusters of 1 9 14 5 and 37 4 42 4 wt nacl eqv respectively this implies that metal precipitation resulted from fluid boiling co2 escape and transient oversaturation the estimated trapping pressures of fis range from 130 to 380 mpa suggesting an alternating lithostatic hydrostatic fluid system controlled by a fault valve at the depth of 13 km therefore the tiemurt pb zn cu deposit is likely an example of orogenic pb zn cu systems formed in collision orogeny rather than a pre collision vms or sedex system developed in devonian and a new metallogenic model is proposed to interpret the formation of the tiemurt pb zn cu deposit

contrasting subduction structures within the philippine sea plate hydrous oceanic crust and anhydrous volcanic arc crust we show contrasting subduction structures within the philippine sea plate inferred from active source wide angle reflection data previous studies showed that large amplitude reflections from the slab are observed in southwest japan and indicated that a thin low velocity layer with a high fluid content is formed along the top of the subducting oceanic crust on the contrary we found that the slab reflections have smaller amplitudes in the izu collision zone central japan where the izu bonin volcanic arc has been colliding subducting suggesting that such a low velocity layer does not exist beneath the collision zone this structural difference is also supported by p wave and s wave velocity anomalies by passive source tomography and electrical conductivity and correlates with the regional distribution of deep tremors and intraslab earthquakes both of which are induced by dehydration processes within the downgoing slab based on these comparisons we suggest that the original structure of the incoming plate controls the contrasting subducting systems typical oceanic plate absorbs water by hydrothermal circulation at spreading centers and or seawater infiltration at outer rises whereas volcanic arc crust consumes a large amount of hydrous minerals for melt production and metamorphoses to more stable anhydrous forms before subduction

plate convergence and long term crustal deformation in central japan surveys by continuous global positioning system in and around japan revealed that the amurian plate collides with the north american plate in central japan by 2 cm yr long term crustal deformation seems to be influenced mainly by this collision although subduction of oceanic plates governs short term elastic deformation over the arc here we study the long term deformation field by carefully removing the short term signals inferred from a priori plate convergence vectors and coupling strengths predicted by a thermal model the obtained field shows that the change in velocities occurs along the longitude 135 137 and there exist a relatively rigid block and zones accommodating strains characteristic compressional deformation is found northwest of izu due possibly to the collision of the izu bonin arc with honshu plate convergence rate along the nankai suruga trough is considerably smaller in eastern parts due partly to the transition from the amurian to the north american plate of the landward side and partly to the motion of the izu microplate relative to the philippine sea plate this accounts for longer recurrence intervals of interplate earthquakes in the suruga trough where the tokai earthquake is anticipated to occur

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses