aftershocks of the 2010 mw 7 2 el mayor cucapah earthquake reveal complex faulting in the yuha desert california 1 we detect and precisely locate over 9500 aftershocks that occurred in the yuha desert region during a 2 month period following the 4 april 2010 mw 7 2 el mayor cucapah emc earthquake events are relocated using a series of absolute and relative relocation procedures that include hypoinverse velest and hypodd location errors are reduced to 40 m horizontally and 120 m vertically aftershock locations reveal a complex pattern of faulting with en echelon fault segments trending toward the northwest approximately parallel to the north american pacific plate boundary and en echelon conjugate features trending to the northeast the relocated seismicity is highly correlated with published surface mapping of faults that experienced triggered surface slip in response to the emc main shock aftershocks occurred between 2 km and 11 km depths consistent with previous studies of seismogenic thickness in the region three dimensional analysis reveals individual and intersecting fault planes that are limited in their along strike length these fault planes remain distinct structures at depth indicative of conjugate faulting and do not appear to coalesce onto a throughgoing fault segment we observe a complex spatiotemporal migration of aftershocks with seismicity that jumps between individual fault segments that are active for only a few days to weeks aftershock rates are roughly consistent with the expected earthquake production rates of dieterich 1994 the conjugate pattern of faulting and nonuniform aftershock migration patterns suggest that strain in the yuha desert is being accommodated in a complex manner

the origin and evolution of skarn forming fluids from the phu lon deposit northern loei fold belt thailand evidence from fluid inclusion and sulfur isotope studies abstract the phu lon skarn cu au deposit is located in the northern loei fold belt lfb thailand it is hosted by devonian volcano sedimentary sequences intercalated with limestone and marble units intruded by diorite and quartz monzonite porphyries phu lon is a calcic skarn with both endoskarn and exoskarn facies in both skarn facies andradite and diopside comprise the main prograde skarn minerals whereas epidote chlorite tremolite actinolite and calcite are the principal retrograde skarn minerals four types of fluid inclusions in garnet were distinguished 1 liquid rich inclusions 2 daughter mineral bearing inclusions 3 salt saturated inclusions and 4 vapor rich inclusions epidote contains only one type of fluid inclusion liquid rich inclusions fluid inclusions associated with garnet prograde skarn stage display high homogenization temperatures and moderate salinities 421 6 468 5 c 17 4 23 1 wt nacl equiv by contrast fluid inclusions associated with epidote retrograde skarn stage record lower homogenization temperatures and salinities 350 9 399 8 c 0 5 8 wt nacl equiv these data suggest a possible mixing of saline magmatic fluids with external dilute fluid sources e g meteoric fluids as the system cooled some fluid inclusions in garnet contain hematite daughters suggesting an oxidizing magmatic environment sulfur isotope determinations on sulfide minerals from both the prograde and retrograde stages show a uniform and narrow range of 34 s values 2 6 to 1 1 34 s suggesting that the ore forming fluid contained sulfur of orthomagmatic origin overall the phu lon deposit is interpreted as an oxidized cu au skarn based on the mineralogy and fluid inclusion characteristics

trace element modelling of pelite derived granites the presence or absence of a vapour phase during incongruent melt reactions of muscovite and biotite together with the composition of the protolith determines the trace element characteristics of the resulting melt provided that equilibrium melting occurs for those phases that host the tracc elements of interest for granitic melts rb sr and ba provide critical constraints on the conditions that prevailed during melting whereas ree are primarily controlled by accessory phase behaviour mass balance constraints for eutectic granites that are formed by the incongruent melting of muscovite in pelites indicate that melting in the presence of a vapour phase will result in a large melt fraction and deplete the restite in feldspar hence the melt will be characterized by low rb sr and high sr ba ratios in contrast vapour absent melting will result in a smaller melt fraction and an increase in the restitic feldspar consequently high rb sr and low sr ba ratios are predicted vapour absent melting will also enhance the negative eu anomaly in the melt granites that result from the incongruent melting of biotite in the source will be characterized by higher rb concentrations than those that result from the incongruent melting of muscovite the himalayan leucogranites provide an example of unfractionated crustally derived eutectic melts that are enriched in rb but depleted in sr and ba relative to their metasedimentary protoliths these compositions may be generated by the incongruent melting of muscovite as a low melt fraction f 0 1 from a pelitic source under vapour absent conditions

late holocene lacustrine chronology and archaeology of ancient lake cahuilla california freshwater lakes existed intermittently in the salton trough of southern california during the late holocene the lakes formed north of the subaerial colorado river delta whenever the colorado river flowed west into the trough instead of south to the gulf of california water filled the trough to a maximum altitude of 12 m stratigraphy radiocarbon dates and supplementary evidence document four lacustral intervals of lake cahuilla between a d 700 and 1580 archaeological sites are associated with the 12 m shoreline and their occupation correlates with these lacustral intervals

the gutenberg richter or characteristic earthquake distribution which is it abstract paleoearthquake and fault slip rate data are combined with the cit usgs catalog for the period 1944 to 1992 to examine the shape of the magnitude frequency distribution along the major strike slip faults of southern california the resulting distributions for the newport inglewood elsinore garlock and san andreas faults are in accord with the characteristic earthquake model of fault behavior the distribution observed along the san jacinto fault satisfies the gutenberg richter relationship if attention is limited to segments of the san jacinto that are marked by the rupture zones of large historical earthquakes or distinct steps in fault trace the observed distribution along each segment is consistent with the characteristic earthquake model the gutenberg richter distribution observed for the entirety of the san jacinto may reflect the sum of seismicity along a number of distinct fault segments each of which displays a characteristic earthquake distribution the limited period of instrumental recording is insufficient to disprove the hypothesis that all faults will display a gutenberg richter distribution when averaged over the course of a complete earthquake cycle but given that 1 the last 5 decades of seismicity are the best indicators of the expected level of small to moderate size earthquakes in the next 50 years and 2 it is generally about this period of time that is of interest in seismic hazard and engineering analysis the answer to the question posed in the title of the article at least when concerned with practical implementation of seismic hazard analysis at sites along these major faults appears to be the characteristic earthquake distribution

earthquake size as a function of fault slip rate abstract estimates of the potential size of earthquakes on mapped active faults are generally based on regressions of earthquake magnitude m w versus length l of fault rupture for historical earthqukes the fault slip rate s has been ignored in formal prediction equations but more accurate predictions of future earthquake magnitudes on mapped faults may be obtained when it is included a least squares regression for a data set of 43 earthquakes occurring on faults for which slip rates are reported shows m w 5 12 1 16 log l 0 20 log s where l is in units of km and s is in units of mm yr the result indicates that the largest earthquakes will occur on the slowest slipping faults if the rupture length is held constant

evidence for prehistoric earthquakes on the superstition hills fault from offset geomorphic features offset geomorphic features along the superstition hills fault show evidence for at least one slip event prior to the 1987 surface rupture and possibly as many as four to five earlier prehistoric earthquakes we documented several geomorphic features that appeared offset by multiple events by making detailed topographic maps offset features were abundant along reaches of the fault with high topographic relief and large displacement slip distribution for the penultimate event as recorded by offset rills streams and shrub coppice dunes is very similar to the slip distribution from the 1987 earthquake through april 1988 this similarity may prove to be fortuitous if afterslip from the 1987 event continues to increase the total slip for this earthquake but if afterslip associated with the 1987 event ceases in the near future then the past two earthquakes were nearly identical in slip and the superstition hills fault may be expected to produce characteristic earthquakes of roughly magnitude 6

rupture patterns and preshocks of large earthquakes in the southern san jacinto fault zone we relocated the large 1937 1942 and 1954 earthquakes in the san jacinto fault zone the epicenters of the main shocks aftershocks and some preshocks were determined using empirical station corrections from recent small events in the study areas the 1937 ml 5 9 earthquake has an epicenter between the surface traces of the san jacinto and buck ridge faults and aftershocks suggest about 7 km of rupture predominantly to the northwest a significant increase in small earthquake activity occurred about formula yr before this event the 1954 m l 6 2 earthquake is located at the southeast end of the mapped trace of the san jacinto fault and aftershocks suggest about 15 km of rupture further southeast into an area of folded young sediments with no surface fault trace this event was preceded by a cluster of small earthquakes which occurred within an 8 hr period 10 weeks before the main event and in the eventual rupture zone the 1942 m l 6 3 earthquake is located southwest of the southeast end of the coyote creek fault large aftershocks of this event are spread over a 15 by 18 km area southwest of the coyote creek fault and are not associated with any one fault the relation of the 1942 event to the san jacinto fault zone is not simple

in situ la mc icp ms and id tims u pb geochronology of cassiterite in the giant furong tin deposit hunan province south china new constraints on the timing of tin polymetallic mineralization abstract the furong deposit located in southern hunan province china is a newly discovered giant tin deposit spatially associated with the a type qitianling granite the petrogenetic link between the giant furong tin deposit and the qitianling granite batholith remains controversial because of the lack of precise dating for the tin polymetallic mineralization here we report for the first time in situ u pb data on cassiterite obtained by la mc icp ms and the results are compared to id tims data the in situ la mc icp ms analyses of the cassiterites provide a reliable age constraint for tin polymetallic mineralization in the furong deposit yielding an isochron age of 159 9 1 9 ma at 95 confidence level mswd 18 which is indistinguishable from the id tims 206 pb 238 u weighted mean age of 158 2 0 4 ma the in situ u pb ages corroborate the ar ar dates published for the furong tin deposit which indicate that the mineralization is coeval with the emplacement of the qitianling granite batholith these results provide further evidence of a close temporal link between the pluton s emplacement and tin mineralization in the furong area the data obtained clearly demonstrate that in situ la mc icp ms u pb dating of cassiterite is a robust geochronometer for direct dating of tin polymetallic mineralization

an evaluation of plate tectonic models for the development of sumatra abstract over the past two decades models have been developed which suggest that the asian continent has been formed since the late palaeozoic by the accretion of continental blocks derived from the northern margin of gondwana sumatra forming the southwestern margin of the southeast asian promontory sundaland is considered to be composed of fragments of continental plates and magmatic arcs which were derived from gondwana during the late palaeozoic and mesozoic the indochina block forms the core of sundaland extending into the eastern part of the malay peninsula the greater part of sumatra is considered to form part of the sibumasu block which accreted to the indochina block along the bentong raub suture in the triassic a model has been proposed in which the southern part of the sibumasu block in the western part of the malay peninsula and sumatra is divided into malacca and mergui microplates by the mutus assemblage which represents another triassic suture a review of the permo triassic stratigraphy of malaya and sumatra provides no support for this model comparison of the permo carboniferous stratigraphy and palaeontology of northern sumatra with that of the malay peninsula and peninsular thailand and in particular the occurrence of tillites links sumatra firmly to the rest of the sibumasu block to the north comparison with the permo carboniferous stratigraphy of bonaparte gulf region of northwest australia shows a mirror image relationship suggesting that the sibumasu block separated from this part of the gondwanan margin in the mid permian on the other hand permo carboniferous rocks in central sumatra contain a cathaysian fauna and flora which relates this area to the indochina block rather than to sibumasu this anomaly was recognised early in the study of the geology of sumatra and led to the proposal of a djambi nappe thrust over sumatra from the east the cathaysian fauna and flora is associated with an early permian volcanic arc it has been suggested that this was an independent island arc accreted to the western margin of sibumasu but from the relationships of the volcanic rocks to permian sediments and the underlying basement it is most probable that this arc was developed on the margin of the cathaysian block the most recently accreted pre tertiary unit on sumatra is the woyla group a jurassic early cretaceous oceanic volcanic arc which together with its associated accretionary complex of oceanic crustal material was thrust over the western margin of sumatra in the mid cretaceous earlier plate models for the development of sumatra are reviewed and a revised model is proposed however there are still many difficulties in interpreting the stratigraphy and the tectonic development of sumatra which will require further detailed study aimed at resolving the many outstanding problems

petrogenesis of malaysian granitoids in the southeast asian tin belt part 1 geochemical and sr nd isotopic characteristics the malaysian granitoids of the southeast asian tin belt have been traditionally divided into a permian to late triassic i type dominated arc related eastern province indochina terrane and a late triassic s type dominated collision related main range province sibumasu terrane separated by the bentong raub paleo tethyan suture that closed in the late triassic the present study however shows that this model is oversimplified and that the direct application of chappell and white s 1974 i and s type classification cannot account for many of the characteristics shared by malaysian granitoids despite being commonly hornblende bearing as is typical for i type granites the roof zones of the eastern province granites are hornblende free in addition the main range province granitoids contain insignificant primary muscovite and are dominated by biotite granites mineralogically similar to many of the plutons of the eastern province in general the malaysian granitoids from both provinces are more enriched in high field strength elements than typical cordilleran i and s type granitoids the mineralogy and geochemistry of the eastern province granitoids and their relationship with contemporaneous volcanics confirm their i type nature the bulk liquid lines of descent of both granitic provinces largely overlap with one another sr nd isotopic data further demonstrate that the malaysian granitoids especially those of the main range were hybridized melts derived from two end member source regions one of which is isotopically similar to the kontum orthoamphibolites and the other akin to the kontum paragneisses of the indochina block however there are differences in the source rocks for the two provinces and it is suggested in this paper that these are related to differing proportions of igneous and sedimentary protoliths the incorporation of sedimentary sourced melts in the eastern province is insignificant which allowed the granites in this belt to maintain their i type nature the presence of minor primary tin mineralization in the eastern province compared to the much more significant tin endowment in the main range is considered to reflect the incorporation of a smaller proportion of sedimentary protolith in the melt products of the former

surface displacement on the imperial and superstition hills faults triggered by the westmorland california earthquake of 26 april 1981 parts of the imperial and the superstition hills faults moved right laterally at the ground surface at the time of or shortly following the ml 5 6 westmorland earthquake of 26 april 1981 the displacements probably occurred before any significant aftershocks on either fault and thus are classed as triggered slips although the main shock was located in an exceptionally seismogenic part of imperial valley about 20 km distant from either fault no clear evidence of past surface faulting is known in the epicentral area horizontal displacement on the imperial and superstition hills faults southeast and southwest of the epicenter respectively reached maxima of 8 and 14 mm and the discontinuous surface ruptures formed along approximately equal lengths of northern segments of the two structures 16 8 and 15 7 km respectively the maximum vertical component of slip measured on surface cracks on the imperial fault 6 mm was located on the west side of mesquite basin near harris road leveling data at harris road suggest slightly larger vertical movement at the surface there fault dislocation modeling of this leveling data further suggests that the maximum shallow subsurface dip slip component of the triggered movement was as much a factor of 4 larger than that measured at the fault trace the map pattern of the rupture may reveal the principal strand among the several near the north end of the imperial fault no surface displacement was found along traces of the brawley fault zone the san andreas fault or the part of the coyote creek fault that slipped during the 1968 borrego mountain earthquake ground search in the epicentral area of the main shock and in the widely dispersed aftershock region in northern imperial valley failed to locate any definite evidence of new surface faulting

the isotopic composition of yb and the precise and accurate determination of lu concentrations and lu hf ratios by isotope dilution using mc icpms 1 we report yb isotopic data for the purpose of accurately correcting measurements of lu and lu hf ratios during multicollector inductively coupled plasma mass spectrometer mc icpms analysis the yb isotopic ratios agree with recent results of chu et al 2002 and amelin and davis 2004 when corrected for mass fractionation to the same reference values protocols for lu measurement involving simultaneous subtraction of yb interference and application of a fractionation correction based on yb are described it is shown that lu concentrations and lu hf ratios determined by mc icpms using this methodology are more precise and potentially more accurate than results based on analysis of lu by thermal ionization mass spectrometry tims a number of mc icpms lu hf isotopic analyses of standard rocks and other geological samples previously analyzed by tims are presented these document reproducibility of lu hf within 0 2 where most discrepancies can be assigned to the unknown lu mass fractionation during tims analysis

ti in zircon thermometry applied to contrasting archean metamorphic and igneous systems abstract ti in zircon thermometry with shrimp ii multi collector has been applied to two well documented archean igneous and metamorphic samples from southern west greenland zircons from 2 71 ga partial melt segregation g03 38 formed in a small 1000 c yield a low temperature focused normal distribution with a mean of 683 32 c further demonstrated by high resolution ti mapping of two individual grains this distribution is interpreted to represent the temperature of the residual magma at zircon saturation late in the crystallization history of the tonalite hypothetically ti in zircon thermometry on eoarchaean detrital zircons sourced from such a high temperature tonalite would present a low temperature biased image of the host magma which could be misconstrued as being a minimum melt granite multiple analyses from individual zircons can yield complex ti distributions and associated apparent temperature patterns reflecting cooling history and local chemical environments in large magma chambers in addition to inclusions and crystal imperfections which can yield apparent high temperature anomalies zircon surfaces can also record extreme 1000 c apparent ti temperatures in our studies these were traced to 49ti or a molecular isobaric interference contamination derived from the double sided adhesive tape used in sample preparation and should not be assigned geological significance

variable rates of late quaternary strike slip on the san jacinto fault zone southern california three strike slip displacements of strata with known approximate ages have been measured at two locations on the san jacinto fault zone minimum horizontal offset between 5 7 and 8 6 km in no more than 0 73 m y northeast of anza indicates 8 12 mm yr average slip rate since late pleistocene time two measures of more recent displacement are based on trenching studies of stratigraphic offsets on the coyote creek fault in western imperial valley horizontal slip of 1 7 m has been calculated for the youngest sediment of lake cahuilla since its deposition 275 510 yr b p the corresponding slip rate is 2 8 5 0 mm yr right lateral offset of 10 9 m measured on a buried stream channel older than 5060 yr b p but younger than 6820 yr b p yields average slip rates for the intermediate time periods 400 to 6000 yr b p of 1 2 mm yr the average rates of slip for these three time intervals suggest a relatively quiescent period for the san jacinto fault zone from about 4000 b c to about 1600 a d to the extent that long term variations in seismic activity of major strike slip faults elsewhere are known fluctuations in slip rate for the san jacinto fault would not appear to be abnormal if the san jacinto and adjacent segments of the san andreas fault alternately assume dominant roles in absorbing motion between the pacific and american plates perhaps even more recently than 400 yr ago the san andreas fault south of the transverse ranges expressed most of the motion but has since become relatively inactive

depth of emplacement fluid provenance and metallogeny in granitic terranes a comparison of western thailand with other tin belts the most important tin mineralization in thailand is associated with the late cretaceous to middle tertiary western thai granite belt a variety of deposit types are present in particular pegmatite vein and greisen styles of mineralization a feature common to most of the deposits is that they are associated with granites that were emplaced into the khang krachan group which consists of poorly sorted carbonaceous pelitic metasediments most of the deposits contain low to moderately saline aqueous fluid inclusions and aqueous carbonic inclusions with variable ch4 co2 ratios low salinity aqueous inclusions represent trapped magmatic fluid in at least one case the nong sua pegmatite based on their occurrence as primary inclusions in magmatic garnet aqueous carbonic inclusions are commonly secondary and neither the co2 nor nacl contents of these inclusions decrease in progressively younger inclusions implying that they are not magmatic in origin reduced carbon is depleted in the metasediments adjacent to granites and the d values greisen muscovites are variable but are as low as 134 per mil indicative of fluid interaction with organic graphitic material this suggests that the aqueous carbonic fluid inclusions represent fluids that were produced at least in part during contact metamorphism metasomatism by comparing the western thai belt with other sn w provinces it is evident that there is a strong correlation between fluid composition and pressure in general low to moderately saline aqueous inclusions and aqueous carbonic inclusions are characteristic of mineralization associated with relatively deep plutonic belts mineralized pegmatites are also typically of deeper plutonic belts and pegmatite hosted deposits may contain cassiterite that is magmatic crystallized from granitic melt or is orthomagmatic hydrothermal crystallized from aqueous or aqueous carbonic fluids in origin the magmatic aqueous fluids those that were exsolved from granitic melts are interpreted to have had low salinities as a consequence of the low salinities tin is partitioned in favour of the melt on vapour saturation thus with a high enough degree of fractionation the crystallization of a magmatic cassiterite or different sn phase such as wodginite is inevitable because tin is not partitioned in favour of the vapour phase upon water saturation of the granitic melts it is proposed that relatively deep vein and greisen systems tend to form by remobilization processes in addition many deeper greisen systems are hosted in part by carbonaceous pelitic metasediments and the reduced nature of the metasediments may play a key role in remobilizing tin sub volcanic systems by contrast are characterized by high temperature high salinity fluids owing to the high chlorinity tin is strongly partitioned in favour of the vapour and cassiterite mineralization can form by of orthomagmatic hydrothermal processes similar relationships between the depth of emplacement and fluid composition also appear to apply to other types of granite hosted deposits such as different types of molybdenum deposits

earthquake recurrence models and historical seismicity in the mexicali imperial valley abstract we have examined the historical seismicity of the mexicali imperial valley since about 1850 the largest observed earthquake in the area has been the magnitude m w 7 1 december 1934 event the magnitude distribution for large plate boundary rupturing earthquakes m 5 8 is not well fit by the gutenberg richter type b value model models which better fit the observed magnitude distribution are derived from a lognormal distribution of stress drops on faults of constant size and from an exponential distribution of rupture lengths as might be expected from randomly distributed rupture stopping asperities along the length of the fault this may be among the best data in the world for testing earthquake recurrence models e g time predictability slip predictability on a strike slip fault but the uncertainties are still too great to permit a unique interpretation

genesis of a magmatic metamorphic hydrothermal system the sn w polymetallic deposits at pilok thailand cassiterite wolframite and base metal mineralization in the pilok area are hosted by veins and stockworks in the apical portion of leucocratic granite stocks close to their contacts with pelitic metasedimentary rocks a minimum pressure of emplacement of approximately 1 500 bars is indicated by the presence of two coexisting feldspars in the granites and a moderate depth is supported by a lack of coeval volcanism and absence of porphyritic textures that characterize hypabyssal intrusions a contact metamorphic metasomatic aureole in the surrounding pelitic metasediments consists of tourmaline biotite and muscovite zones that are superimposed on muscovite chlorite zone regional metamorphism whole rock carbon analyses demonstrate a volatilization of graphite in the metasediments as a function of distance from the intrusion and the presence of andalusite in the aureole constrains the maximum pressure to approximately 3 800 bars the earliest mineralization is late magmatic to early postmagmatic wolframite cassiterite intergrown with li and f rich muscovite in pegmatite pods the bulk of the wolframite mineralization was subsequently deposited in veins with potassic alteration which could have originated either by orthomagmatic or remobilization processes finally cassiterite and sulfides chalcopyrite sphalerite were deposited in association with greisen alteration and formed as a result of the remobilization of tin from the host granite fluid inclusion and stable isotope data indicate the involvement of at least four fluid types a moderately saline fluid of presumed magmatic origin aqueous carbonic metamorphic fluids low temperature and low salinity meteoric fluids and high salinity formational or metamorphic fluids the isotopic compositions of waters calculated from delta o 18 analyses of quartz muscovite and cassiterite and delta d analyses of muscovite range from 1 4 to 9 4 and 63 to 118 per mil respectively these are consistent with the mixing of magmatic and organic rich metamorphic fluids oxygen isotope thermometry indicates temperatures of 350 degrees to 500 degrees c for cassiterite mineralization the oldest preserved fluid inclusions are primary aqueous carbonic inclusions from wolframite and cassiterite mineralization both the homogenization of the carbonic phase and the bulk

intermediate term pre earthquake phenomena in california 1975 1986 and preliminary forecast of seismicity for the next decade intermediate term observations preceding earthquakes of magnitude 5 7 or greater in california from 1975 through 1986 suggest that 1 the sudden appearance of earthquakes in a previously inactive area indicates an increased likelihood of a significant earthquake in that area for a period from days to years 2 these larger earthquakes tend to occur towards the ends of creeping fault segments 3 one large earthquake in a region increases the likelihood of a subsequent significant event in the adjacent area and 4 marginal evidence for the occurrence of a regional deformation event suggests that such events increase the probability of earthquake occurrence throughout the entire area a common element in many of these observed patterns appears to be the transmission and amplification of tectonic stress changes by the mechanism of fault creep and suggests that surface fault creep is a sensitive indicator of changes in stress the preceding critieria are used to construct a preliminary forecast of the likely locations of significant earthquakes over the next decade

fault slip rates and earthquake histories for active faults in southern california abstract within the context of the historical record of seismicity we review the geological data bearing on the quaternary slip rates and paleoearthquake histories of active faults in southern california

the permian fusulinoidean faunas of the sibumasu and baoshan blocks their implications for the paleogeographic and paleoclimatologic reconstruction of the cimmerian continent abstract permian fusulinoidean faunas occur in mainly four stratigraphic levels in the baoshan block of west yunnan and the sibumasu block of southeast asia which constituted part of the eastern cimmerian continent the oldest fauna from the upper part of the dingjiazhai formation in the baoshan block consists of pseudofusulina eoparafusulina and a new boultoniid genus and is assignable to the yakhtashian artinskian the second one which occurs in the basal part of the ratburi limestone and its equivalent strata in the sibumasu block is represented by monodiexodina and is probably referable to the bolorian kungurian the third fauna composed of eopolydiexodina rugososchwagerina yangchienia chusenella jinzhangia and several other genera is dated to the murgabian wordian and occurs in the lower part of the shazipo and daaozi formations in the baoshan block and the main part of the ratburi limestone in the sibumasu block the youngest fauna of probably dzhulfian wuchiapingian age is found in the upper part of the ratburi limestone and contains nanlingella reichelina codonofusiella and a few staffellid genera a smaller foraminiferal genus shanita found from the upper part of the ratburi limestone and the upper part of the shazipo formation is also an important element of the foraminiferal assemblage near the midian dzhulfian capitanian wuchiapingian boundary in the baoshan and sibumasu blocks in the eastern cimmerian continent low generic diversity throughout the permian and the paucity of tethys characterizing neoschwagerinid and verbeekinid genera during middle permian time are two remarkable features of the permian fusulinoidean faunas in the cimmerian continent the generic diversity of permian fusulinoidean faunas in space and time gradually increases from the early permian to late middle permian as well as from the eastern cimmerian areas to western ones the temporal increase of the generic diversity can be explained by the northward drift of the cimmerian continent during permian time in contrast the lower generic diversity of the eastern cimmerian permian fusulinoidean faunas against western ones is possibly due to an oblique arrangement of the continent to paleolatitude thus the western cimmerian continent was more proximal to the tropical tethyan domain than its eastern part in addition the middle permian cimmerian paleobiogeographic region is likely to be subdivided into two subregions the western tethyan cimmerian and the eastern gondwanan cimmerian based on the distribution pattern of verbeekinid and neoschwagerinid fusulinoideans and overall generic diversity the scarce occurrence or total absence of these essentially tethys indicating fusulinoideans in the baoshan and sibumasu blocks suggests that the eastern cimmerian continent was still far from the equatoro tropical cathaysian domain and was probably in a warm temperate or subtropical zone until the end of the permian the eastern cimmerian areas finally migrated into a tropical zone by the late triassic judging from well developed carnian sponge coral buildups in the chaiburi formation in the sibumasu block

relative oxidation states of magmas inferred from ce iv ce iii in zircon application to porphyry copper deposits of northern chile major and trace element compositions of zircons and whole rocks from 14 barren and seven ore bearing calc alkaline intrusions from the chuquicamata el abra porphyry copper belt of northern chile have been measured in situ by excimer laser ablation ela icp ms these data permit the ce iv ce iii ratio within zircon to be calculated using a lattice strain model for mineral melt partitioning of ce iv and ce iii zircon ce iv ce iii and eun eun ratios and by inference magmatic oxidation states generally increase from older mafic to younger felsic units within this sequence porphyry copper mineralization is directly associated only with intrusions with zircon ce iv ce iii 300 and eun eun 0 4 such trends can be understood in terms of interdependent relations between oxygen fugacity sulfur speciation and solubility and chalcophile element partitioning in silicate magmas because zircon occurs in most calc alkaline intrusions and is resistant to subsolidus alteration zircon ce iv ce iii ratios provide a useful tool for evaluating the economic potential of such rocks for magmatic hydrothermal cu au mineralization the approach is general and may provide a means to infer relative oxidation state in a wide range of intermediate to felsic igneous rocks

on the modelling of two dimensional aeolian dunes in this study the modelling of aeolian dunes is treated from the background of the physical processes that form them the paper concentrates on two dimensional modelling which can be applied to transverse and barchan dunes the basic assumptions and equations are discussed and three models are presented a a kinematic model which is based on a linear variation of the sediment transport with the topographic height b an analytical model based on a boundary layer model of the wind velocity and bagnold s linearized sediment transport formula c a generalization of this analytical model in a computer program which includes a simple routine for simulating the redistribution of sediment through avalanching the relative importance of the simplifications is considered and indications are given for the practical applications of these three models in field studies

cretaceous cenozoic tectonic events in the western myanmar burma assam region correlation of late mesozoic mafic and ophiolitic rocks suggests that in the late lower cretaceous a northeasterly facing mafic arc was emplaced onto southeast borneo western sumatra western myanmar burma then 1100 km south of its present position the mogok belt of myanmar and the denqen bangong co ophiolite zone in tibet all then situated on the southwestern margin of asia reversal in tectonic polarity and eastward subduction generated a late cretaceous magmatic arc in western myanmar and sumatra and its continuation through the mogok belt into the gandise batholith of tibet magmatism interrupted in the latest cretaceous probably resumed in the western myanmar tibet and sumatra arc segments in the early palaeogene it was again interrupted in the mid eocene when an east vergent ophiolite nappe overrode the indo burman ranges deforming lower eocene turbidites derived from the magmatic arc to the east following renewed northward and eastward subduction of ocean floor in the latest eocene india collided with northern myanmar and with tibet along a suture south of the jurassic triassic flysch and adjacent yarlung ophiolite in the mogok segment of the late cretaceous arc crust thickened in the early cretaceous orogeny underwent extension to form a metamorphic core complex as myanmar west of the sagaing fault moved northward more than half of this northward movement preceded the well documented 450 km of post early miocene dextral displacement on the sagaing fault and related spreading in the andaman sea generation of late cretaceous to early eocene i and s type granites in and east of the mogok belt was related either to crustal shortening or more probably to subsequent extension in the mogok belt

tectonic evolution of the malay peninsula abstract the malay peninsula is characterised by three north south belts the western central and eastern belts based on distinct differences in stratigraphy structure magmatism geophysical signatures and geological evolution the western belt forms part of the sibumasu terrane derived from the nw australian gondwana margin in the late early permian the central and eastern belts represent the sukhothai arc constructed in the late carboniferous early permian on the margin of the indochina block derived from the gondwana margin in the early devonian this arc was then separated from indochina by back arc spreading in the permian the bentong raub suture zone forms the boundary between the sibumasu terrane western belt and sukhothai arc central and eastern belts and preserves remnants of the devonian permian main palaeo tethys ocean basin destroyed by subduction beneath the indochina block sukhothai arc which produced the permian triassic andesitic volcanism and i type granitoids observed in the central and eastern belts of the malay peninsula the collision between sibumasu and the sukhothai arc began in early triassic times and was completed by the late triassic triassic cherts turbidites and conglomerates of the semanggol formation were deposited in a fore deep basin constructed on the leading edge of sibumasu and the uplifted accretionary complex collisional crustal thickening coupled with slab break off and rising hot asthenosphere produced the main range late triassic earliest jurassic s type granitoids that intrude the western belt and bentong raub suture zone the sukhothai back arc basin opened in the early permian and collapsed and closed in the middle late triassic marine sedimentation ceased in the late triassic in the malay peninsula due to tectonic and isostatic uplift and jurassic cretaceous continental red beds form a cover sequence a significant late cretaceous tectono thermal event affected the peninsula with major faulting granitoid intrusion and re setting of palaeomagnetic signatures

fault slip in southern california measurements of slip on major faults in southern california have been performed over the past 18 yr using principally theodolite alignment arrays and tautwire extensometers they provide geodetic control within a few hundred meters of the fault traces which complements measurements made by other techniques at larger distances approximately constant slip rates of from 0 5 to 5 mm yr over periods of several years have been found for the southwestern portion of the garlock fault the banning and san andreas faults in the coachella valley the coyote creek fault the superstition hills fault and an unnamed fault 20 km west of el centro these slip rates are typically an order of magnitude below displacement rates that have been geodetically measured between points at greater distances from the fault traces exponentially decaying postseismic slip in the horizontal and vertical directions due to the 1979 imperial valley earthquake has been measured it is similar in magnitude to the coseismic displacements analysis of seismic activity adjacent to slipping faults has shown that accumulated seismic moment is insufficient to explain either the constant or the decaying postseismic slip thus the mechanism of motion may differ from that of slipping faults in central california which move at rates close to the plate motion and are accompanied by sufficient seismic moment seismic activity removed from the slipping faults in southern california may be driving their relatively aseismic motion

the elmore ranch and superstition hills earthquakes of 24 november 1987 introduction to the special issue on 24 november 1987 two significant earthquakes occurred along the southern san jacinto fault zone and related structural elements in southern california not far from the international border these two events the elmore ranch earthquake m 6 2 at 0154 gmt and the superstition hills earthquake m 6 6 at 1315 gmt both moment magnitudes from sipkin 1989 and their aftershocks have yielded a rich harvest of geological seismological and engineering data pertinent to the cause and effect of earthquakes in this region where the southern san jacinto fault zone enters the salton depression from the peninsula ranges bordering it on the southwest fig 1 this special issue of the bulletin presents 18 geologic and seismologic investigations of these earthquakes a collection of papers born in el centro california on 8 and 9 february 1988 at a meeting attended by approximately 60 scientists interested in these earthquakes for one reason or another

the granites of the southeast asian tin belt four granite provinces have been delineated each with its own distinctive pattern of mineralization 1 the main range province endogenous greisen bordered vein swarms of cassiterite and wolframite 2 the eastern province magnetite cassiterite skarns base metal sulphides with antimony in thailand 3 the western peninsular thailand burma province endogenous greisen bordered vein swarms and pegmatites of cassiterite and wolframite 4 the north thailand migmatitic province endogenous vein and skarn replacement scheelite and fluorite deposits with some tin and local antimony in all provinces but particularly in the main range granitoids designated as two phase variants have been recognized where xenocrysts and xenoliths of coarse primary texture granite are enclosed in and corroded by an invasive equigranular quartzo feldspathic matrix these rocks form an essential part of the granite sequence in all provinces and have probably resulted from the infiltration and disruption of the host granite by late stage magmatic fluids whole rock geochemistry from peninsular malaysia shows that the granites from the main range and eastern provinces comprise two contrasted suites which correspond approximately to the i and s type categories advocated by chappell white 1974 in addition it is shown that individual plutons within batholiths in the two provinces have distinctive geochemical parameters variation diagrams of plutons having the intrusive sequence primary texture granite two phase granite microgranite show linear trends with increasing sio 2 na 2 o rb w sn and u and decreasing sr ba th and all other major elements

reply to comment to short communication ʽcomment hf isotope heterogeneity in zircon 91500 by w l griffin n j pearson e a belousova and a saeed chemical geology 233 2006 358 363 by f corfu

seismic evidence for conjugate slip and block rotation within the san andreas fault system southern california the pattern of seismicity in southern california indicates that much of the activity is presently occurring on secondary structures several of which are oriented nearly orthogonal to the strikes of the major through going faults slip along these secondary transverse features is predominantly left lateral and is consistent with the reactivation of conjugate faults by the current regional stress field near the intersection of the san jacinto and san andreas faults however these active left lateral faults appear to define a set of small crustal blocks which in conjunction with both normal and reverse faulting earthquakes suggests contemporary clockwise rotation as a result of regional right lateral shear other left lateral faults representing additional rotating block systems are identified in adjacent areas from geologic and seismologic data many of these structures predate the modern san andreas system and may control the pattern of strain accumulation in southern california geodetic and paleomagnetic evidence confirm that block rotation by strike slip faulting is nearly ubiquitous particularly in areas where shear is distributed and that it accommodates both short term elastic and long term nonelastic strain a rotating block model accounts for a number of structural styles characteristic of strike slip deformation in california including variable slip rates and alternating transtensional and transpressional features observed along strike of major wrench faults domains of evenly spaced antithetic faults that terminate against major fault boundaries continued development of bends in faults with large lateral displacements anomalous focal mechanisms and differential uplift in areas otherwise expected to experience extension and subsidence since block rotation requires a detachment surface at depth to permit rotational movement low angle structures like detachments of either local or regional extent may be involved in the contemporary strike slip deformation of southern california a block nature of the crust also implies that not only will strains be inhomogeneous and likely concentrated along edge bounding faults but that local stress orientations will largely be responding to local kinematic constraints of block rotation and fault interaction this behavior coupled with the presence of possible regional detachments accounts for some of the precursory changes observed at considerable distances prior to large earthquakes and the triggering of seismicity or slip on nearby faults or around adjacent block edges although fault displacements along secondary structures associated with block rotations remain small they may still influence the nucleation and the characteristic rupture length of large earthquakes a more complete description of what these structures are and how they interact may prove critical to any fundamental understanding of the earthquake process and any realistic assessment of the regional seismic hazard

rupture process of the ms 6 6 superstition hills california earthquake determined from strong motion recordings application of tomographic source inversion abstract we analyze strong motion recordings of the m s 6 6 superstition hills earthquake to determine the timing location spatial extent and rupture velocity of the subevents that produced the bulk of the high frequency 0 5 to 4 hz seismic energy radiated by this shock the earthquake can be characterized by three principal subevents the largest ones occurring about 3 and 10 sec after initiation of rupture timing relationships between pulses on the seismograms indicate that the three subevents are located within 8 km of each other along the northern portion of the superstition hills fault the two largest subevents display different directivity effects we apply a tomographic source inversion to the integrated accelerograms to determine the slip acceleration on the fault as a function of time and distance based on a one dimensional fault model the azimuthal distribution of amplitudes for the second subevent can be largely explained by a rupture that propagated about 2 km to the southeast along the superstition hills fault at a velocity about equal to the p wave velocity an alternative model with rupture propagating to the northeast along a conjugate fault plane can also account for the observed directivity of this subevent but it is not supported by the aftershock distribution the third subevent ruptured to the southeast along an 8 km long portion of the superstition hills fault at about the shear wave velocity this rupture propagation caused the relatively large accelerations and velocities observed in strong motion records for stations southeast of the hypocenter the long time intervals between the subevents and their relative proximity to each other indicate a very slow component to the rupture development the southern half of the superstition hills fault did not generate significant high frequency strong ground motion although it showed substantial co seismic surface displacement the subevents are situated along the same northern portion of the fault where most of the aftershocks are located the locations of the subevents appear to be controlled by bends in the fault mapped at the surface and by changes in basement structure at depth

genesis of granitoid batholiths of peninsular malaysia and implications for models of crustal evolution evidence from a ndsr isotopic and upb zircon study nd sr and u pb isotopic data for the late triassic west coast province batholiths and permian to triassic east coast province batholiths of peninsular malaysia allow estimates of the ages of the crustal fragments comprising the peninsula to be made initial nd and sr values for granitoids from the west coast province range from 6 to 10 and 160 0 716 to 660 0 751 respectively nd model ages calculated based on a depleted mantle evolution model tdmnd range from 1300 ma to 1800 ma and are in general agreement with the mid proterozoic upper intersection ages of u pb zircon reverse discordia 1500 1700 ma initial nd and sr values for granitoids from the east coast province range from 0 8 to 6 and 10 0 705 to 130 0 714 respectively calculated tdmnd ages of 900 1400 ma for these granitoids are comparable to two u pb zircon reverse discordia intercepts that yield 800 ma and 1350 ma the general agreement of u pb zircon inheritance ages and tdmnd ages are interpreted to correspond to the proterozoic crust formation ages of the continental fragments represented by the west coast and east coast batholithic provinces mid proterozoic 1300 1900 ma crust formation ages are commonly shown by other phanerozoic continental margin plutonic and volcanic belts the ubiquitous mid proterozoic crust formation ages and the absence of archaean signatures suggest voluminous juvenile additions to the continental crust in the mid proterozoic such ages at continental margins would imply that many continental blocks had achieved very much their present day extent by the mid proterozoic

earthquakes quaternary faults and seismic hazard in california data describing the locations slip rates and lengths of quaternary faults are the primary basis in this work for constructing maps that characterize seismic hazard in california the expected seismic moment m0e and the strength of ground shaking resulting from the entire rupture of each mapped fault or fault segment are estimated using empirical relations between seismic moment m0 rupture length source to site distance and strong ground motions assuming a fault model whereby the repeat time t of earthquakes on each fault equals m0e m0g where the moment rate m0g is proportional to fault slip rate it is observed that the moment frequency distribution of earthquakes predicted from the geologic data agrees well with the distribution determined from a 150 year historical record the agreement is consistent with the argument that the geologic record of quaternary fault offsets contains information sufficient to predict the average spatial and size distribution of earthquakes through time in california the estimates of t for each fault are the foundation for constructing maps that depict the average return period of 0 1g peak horizontal ground accelerations and the horizontal components of peak acceleration peak velocity and the pseudovelocity response at 1 period and 5 damping expected to occur at the level of 0 1 probability during a 50 year period of time a map is also formulated to show the probability that 0 1g horizontal ground accelerations will occur during the next 50 years the maps serve to illustrate the potential value of quaternary fault studies for assessing seismic hazard interpretation of available slip rates indicates that the largest and most frequent occurrence of potentially destructive strong ground motions are associated principally with the san andreas san jacinto calaveras hayward and ventura basin fault zones other regions of similarly high hazard may yet remain unrecognized this inadequacy results primarily from an incomplete data set numerous faults for example are mapped along the coastal region of northern california and within the modoc plateau but relatively few studies relating to fault slip rate are reported a similar problem exists for other stretches of coastal california where marine reflection studies provide evidence of active faulting offshore yet yield little or no information of fault slip rate geological and geophysical field studies can work to remove these deficiencies a concerted effort to locate and define rates of activity on all faults in california is the most promising means to further quantify present levels of seismic hazard in california

the bentong raub suture zone abstract it is proposed that the bentong raub suture zone represents a segment of the main devonian to middle triassic palaeo tethys ocean and forms the boundary between the gondwana derived sibumasu and indochina terranes palaeo tethyan oceanic ribbon bedded cherts preserved in the suture zone range in age from middle devonian to middle permian and melange includes chert and limestone clasts that range in age from lower carboniferous to lower permian this indicates that the palaeo tethys opened in the devonian when indochina and other chinese blocks separated from gondwana and closed in the late triassic peninsular malaysia segment the suture zone is the result of northwards subduction of the palaeo tethys ocean beneath indochina in the late palaeozoic and the triassic collision of the sibumasu terrane with and the underthrusting of indochina tectonostratigraphic palaeobiogeographic and palaeomagnetic data indicate that the sibumasu terrane separated from gondwana in the late sakmarian and then drifted rapidly northwards during the permian triassic during the permian subduction phase the east malaya volcano plutonic arc with i type granitoids and intermediate to acidic volcanism was developed on the margin of indochina the main structural discontinuity in peninsular malaysia occurs between palaeozoic and triassic rocks and orogenic deformation appears to have been initiated in the upper permian to lower triassic when sibumasu began to collide with indochina during the early to middle triassic a type subduction and crustal thickening generated the main range syn to post orogenic granites which were emplaced in the late triassic early jurassic a foredeep basin developed on the depressed margin of sibumasu in front of the uplifted accretionary complex in which the semanggol formation rocks accumulated the suture zone is covered by a latest triassic jurassic and cretaceous mainly continental red bed overlap sequence

a silent mw 4 7 slip event of october 2006 on the superstition hills fault southern california 1 during october 2006 the 20 km long superstition hills fault shf in the salton trough southern california slipped aseismically producing a maximum offset of 27 mm as recorded by a creepmeter we investigate this creep event as well as the spatial and temporal variations in slip history since 1992 using ers 1 2 and envisat satellite data during a 15 year period steady creep is punctuated by at least three events the first two events were dynamically triggered by the 1992 landers and 1999 hector mine earthquakes in contrast there is no obvious triggering mechanism for the october 2006 event field measurements of fault offset after the 1999 and 2006 events are in good agreement with the interferometric synthetic aperture radar data indicating that creep occurred along the 20 km long fault above 4 km depth with most of the slip occurring at the surface the moment released during this event is equivalent to a mw 4 7 earthquake this event produced no detectable aftershocks and was not recorded by the continuous gps stations that were 9 km away modeling of the long term creep from 1992 to 2007 creep using stacked ers 1 2 interferograms also shows a maximum creep depth of 2 4 km with slip tapering with depth considering that the sediment thickness varies between 3 km and 5 km along the shf our results are consistent with previous studies suggesting that shallow creep is controlled by sediment depth perhaps due to high pore pressures in the unconsolidated sediments

a routine high precision method for lu hf isotope geochemistry and chronology a method for chemical separation of lu and hf from rock meteorite and mineral samples is described together with a much improved mass spectrometric running technique for hf this allows i geo and cosmochronology using the176lu 176hf decay scheme and ii geochemical studies of planetary processes in the earth and moon chemical yields for the three stage ion exchange column procedure average 90 for hf chemical blanks are 0 2 ng for lu and hf from 1 g of hf a total ion current of 0 5 10 11 ampere can be maintained for 3 5 h yielding 0 01 0 03 precision on the ratio176hf 177hf normalisation to179hf 177hf 0 7325 is used extensive results for the johnson matthey hf standard jmc 475 are presented and this sample is urged as an international mass spectrometric standard suitable aliquots prepared from a single batch of jmc 475 are available from denver lu hf analyses of the standard rocks bcr 1 and jb 1 are given the potential of the lu hf method in isotope geochemistry is assessed

fault trace complexity cumulative slip and the shape of the magnitude frequency distribution for strike slip faults a global survey summary we examine whether the shape of the magnitude frequency distribution for strike slip faults is described by the gutenburg richter relationship log n a bm or by the characteristic earthquake model by analysing a data set of faults from california mexico japan new zealand china and turkey for faults within regional seismic networks curves of the form log n yrpl a bm where n yr is the number of events per year equal to magnitude m are fit to the instrumental record of seismicity and geological data are used to estimate independently the size and recurrence rate of the largest expected earthquakes that would rupture the total length of the fault extrapolation of instrumentally derived curves to larger magnitudes agrees with geological estimates of the recurrence rate of the largest earthquakes for only four of the 22 faults if uncertainties in curve slope are considered and significantly underestimates the geological recurrence rates in the remaining cases also if we predict the seismicity of the faults as a function of fault length and slip rate and the predicted seismicity is distributed in accord with the gutenburg richter relationship we find the predicted recurrence rate to be greater than the observed recurrence rates of smaller earthquakes along most faults if individual fault zones satisfy the gutenburg richter relationship over the long term our observations imply that during the recurrence interval of the largest expected earthquakes the recurrence of lesser sized events is not steady but rather strongly clustered in time however if the instrumental records provide an estimate of the long term rate of small to moderate earthquakes along the faults our observations imply that the faults generally exhibit a magnitude frequency distribution consistent with the characteristic earthquake model also we observe that the geometrical complexity of strike slip faults is a decreasing function of cumulative strike slip offset the four faults we observe to be consistent with the gutenburgrichter relationship are among those characterized by the least amount of cumulative slip and greatest fault trace complexity we therefore suggest that the ratio of the recurrence rate of small to large earthquakes along a fault zone may decrease as slip accumulates and the fault becomes smoother

linking the indochina block and gondwana during the early paleozoic evidence from u pb ages and hf isotopes of detrital zircons abstract to constrain the paleoposition of indochina within gondwana during the early paleozoic we performed in situ u pb and hf isotope analyses on detrital zircons from three river sediment samples in the truong son belt of the indochina block the age distributions yield dominant neoarchean 2 5 ga mesoproterozoic 1 7 1 4 ga grenvillian 0 95 ga and pan african 0 65 0 5 ga age groups and minor paleo to meso archean zircons hf isotope compositions of zircons for each age group exhibit large ranges of ehf t suggesting that the zircon host rocks have diverse sources the oldest hf model ages for zircons of neoarchean grenvillian and pan african age group yield 3 7 ga or older while those of mesoproterozoic age group show 3 3 ga the remarkable similarity of age distribution and hf isotope compositions among detrital zircons of indochina and those of tethyan himalaya western cathaysia and qiangtang suggests that indochina was located outboard of qiangtang and south of south china in the indian margin of gondwana during the early paleozoic our results are consistent with the paleontological correlations of east gondwana margin during the early paleozoic

the closure of palaeo tethys in eastern myanmar and northern thailand new insights from zircon u pb and hf isotope data abstract two of the major granite belts of southeast asia are the main range and eastern province together these are interpreted to represent the magmatic expression of the closure of palaeo tethys during late palaeozoic to early mesozoic times recent geochronological and geochemical work has better delineated these belts within peninsular malaysia thereby providing important constraints on the timing of palaeo tethys suturing however the northern extension of this palaeo tethyan suture is less well understood here we present new ion microprobe u pb zircon age data from northern thailand and eastern myanmar measured ages of 219 and 220 ma from the kyaing tong granite imply northern extension of the main range province into eastern myanmar the tachileik granite in far eastern myanmar yields an age of 266 ma consistent with published eastern province ages and this therefore constrains the northern extension of the palaeo tethys suture in eastern myanmar we further discuss how this suture may extend northwards into yunnan a late cretaceous age 70 ma measured in thailand represents later magmatic activity and is similar to published magmatic ages from central myanmar this younger magmatism is interpreted to be related to the subduction of neo tethys prior to india asia collision further we present new laser ablation zircon hf isotope data from eastern myanmar which suggest that palaeoproterozoic crust underlies both the main range and eastern province granites our ehf model age of ca 1750 ma from sibumasu the basement underlying eastern myanmar lies within the range of other model ages reported thus far for the baoshan block north in yunnan interpreted by some to be the northern extension of sibumasu

geochronology and magmatic oxygen fugacity of the tongcun molybdenum deposit northwest zhejiang se china the tongcun mo porphyry deposit in northwest zhejiang is hosted in three porphyry units huangbaikeng songjiazhuang and tongcun from southwest to northeast u pb zircon ages of 162 3 0 ma for the huangbaikeng porphyry 159 9 3 0 ma for the songjiazhuang porphyry and 167 6 155 6 ma for the tongcun porphyry indicate that these intrusions formed during the jurassic and are most likely associated with the northwestward subduction of the izanagi plate trace element compositions of zircons from the tongcun deposit constrain the oxygen fugacity fo2 of the magma using zircon ce anomalies and ti in zircon temperatures the average magmatic fo2 for the porphyries in the tongcun deposit is fayalite magnetite quartz fmq 2 7 which is similar to the shapinggou fmq 3 2 and dabaoshan fmq 3 5 mo porphyry deposits but much higher than that of the reduced cretaceous ore barren shangjieshou porphyry fmq 1 1 around 8 km away from the tongcun deposit the distinct difference in magmatic oxygen fugacity between the jurassic and cretaceous porphyries may help to explain the absence of mo porphyry mineralization in northwest zhejiang during the cretaceous

probabilities of occurrence of large plate rupturing earthquakes for the san andreas san jacinto and imperial faults california 1983 2003 the san andreas san jacinto and imperial faults in california are divided into 19 segments conditional probabilities are calculated that a particular segment will be the site of a large plate rupturing earthquake i e an event that breaks the entire down dip extent of the seismogenic zone during the next 20 years the sizes of such events which account for most of the slip that occurs seismically appear to vary greatly for different segments of these faults repeat time of large shocks coseismic displacement moment release rupture length and seismic magnitude appear to correlate with one another and to be a function of the tectonic style of different parts of those fault zones tectonic inhomogeneities on a scale of about 1 to 100 km are much larger than displacement in any single seismic event and may be regarded as being invariant in their effects upon earthquake generation over many cycles of large shocks it is this invariance that appears to lead to a given segment of a fault rupturing repeatedly in events of nearly the same size since repeat time varies however for a given segment of a fault a simple probabilistic approach is used to forecast the likelihood of large future earthquakes for each segment using as input the time of the last large shock the average recurrence time and the standard deviation of time intervals between events dates of the last large shocks are available for most of the segments investigated repeat times are estimated from times of historic and prehistoric events tectonic similarity and times calculated from coseismic displacement in the last large shock divided by a rate of fault motion or strain buildup the standard deviation of time intervals divided by the average repeat time is close to 1 3 for three fault segments in california for which data are available on historic and prehistoric earthquakes that normalized value is adopted for all calculations of conditional probability magnitudes and seismic moments of future plate rupturing events are estimated for each fault segment several of the segments have well constrained probabilities for rupture during the next 20 years whereas others have large uncertainties eight of the segments constituting about 40 of the total lengths of the three faults have moderate to high probability and thus should be instrumented and studied extensively so as to provide shorter time warnings in some cases two adjacent segments may be nearly in phase in their loading history and may break in a single event the segment of the san andreas fault from opposite san jose to san juan bautista which ruptured less than 1 5 m in 1906 and which probably also broke in 1838 is calculated to have a moderate to high probability of an earthquake of magnitude 6 to during the next 20 years a 325 km section of the southern san andreas between tejon pass and the salton sea has about a 25 chance of rupturing in a shock of magnitude near 8 during the next 20 years all the other segments have only a small chance i e less than 5 to 10 of rupturing in an event of magnitude near 8 during that interval

irregular recurrence of large earthquakes along the san andreas fault evidence from trees old trees growing along the san andreas fault near wrightwood california record in their annual ring width patterns the effects of a major earthquake in the fall or winter of 1812 to 1813 paleoseismic data and historical information indicate that this event was the san juan capistrano earthquake of 8 december 1812 with a magnitude of 7 5 the discovery that at least 12 kilometers of the mojave segment of the san andreas fault ruptured in 1812 only 44 years before the great january 1857 rupture demonstrates that intervals between large earthquakes on this part of the fault are highly variable this variability increases the uncertainty of forecasting destructive earthquakes on the basis of past behavior and accentuates the need for a more fundamental knowledge of san andreas fault dynamics

slip on the superstition hills fault and on nearby faults associated with the 24 november 1987 elmore ranch and superstition hills earthquakes southern california alignment arrays and creepmeters spanning several faults in southern california recorded slip associated with the 24 november 1987 elmore ranch and superstition hills earthquakes no precursory slip had occurred on the superstition hills fault up to 27 october 1987 when the last measurement before the earthquakes was made about 23 days before the earthquake dextral creep events of about 13 mm and 0 5 mm may have occurred simultaneously on the imperial and southern san andreas faults respectively but the tectonic origin of the smaller event is questionable within 12 hr after the superstition hills earthquake 20 9 cm of dextral slip occurred on the main fault trace at the superstition hills alignment array and 39 8 cm of dextral slip was recorded over the entire 110 m width of the array despite this initial wide distribution of slip nearly all of the postseismic slip is occurring on the main fault trace as of 3 august 1988 the alignment array had recorded a total of 80 2 cm of dextral slip as of 5 days after the earthquakes 65 to 80 per cent of the total slip measured by the alignment array had occurred on discrete mappable fractures in addition the two earthquakes triggered slip on the coyote creek fault the southern san andreas fault and on the imperial fault telemetered data from creepmeters on the southern san andreas and imperial faults indicate that triggered slip began there within 3 min or less of each of the two earthquakes additional triggered slip occurred on the imperial fault beginning 3 5 hr after the second earthquake

a more precise chronology of earthquakes produced by the san andreas fault in southern california improved methods of radiocarbon analysis have enabled us to date more precisely the earthquake ruptures of the san andreas fault that are recorded in the sediments at pallett creek previous dates of these events had 95 confidence errors of 50 100 calendar years new error limits are less than 23 calendar years for all but two of the dated events this greater precision is due to larger sample size longer counting time lower background noise levels more precise conversion of radiocarbon ages to calendric dates and better stratigraphic constraints and statistical techniques the new date ranges with one exception fall within the broader ranges estimated previously but our estimate of the average interval between the latest 10 episodes of faulting is now about 132 years variability about the mean interval is much greater than was suspected previously five of the nine intervals are shorter than a century three of the remaining four intervals are about two to three centuries long despite the wide range of these intervals a pattern in the occurrence of large earthquakes at pallett creek is apparent in the new data the past 10 earthquakes occur in four clusters each of which consists of two or three events earthquakes within the clusters are separated by periods of several decades but the clusters are separated by dormant periods of two to three centuries this pattern may reflect important mechanical aspects of the fault s behavior if this pattern continues into the future the current period of dormancy will probably be greater than two centuries this would mean that the section of the fault represented by the pallett creek site is currently in the middle of one of its longer periods of repose between clusters and sections of the fault farther to the southeast are much more likely to produce the next great earthquake in california the greater precision of dates now available for large earthquakes recorded at the pallett creek site enables speculative correlation of events between paleoseismic sites along the southern half of the san andreas fault a history of great earthquakes with overlapping rupture zones along the mojave section of the fault remains one of the more attractive possibilities

a 300 to 550 year history of slip on the imperial fault near the u s mexico border missing slip at the imperial fault bottleneck subsurface investigation of the imperial fault zone approximately 50 60 m south of the u s mexico international border in mexicali valley reveals that only the 1940 imperial valley earthquake m l 7 1 has produced significant surface slip in the past 300 years the 1940 earthquake produced about 5 m of slip in this vicinity as indicated by an offset tree line we excavated a buried channel adjacent to these trees and determined that it is also offset 5 m these data indicate that at least the upper meter of sediments has only been displaced by the 1940 event one other slip event of undetermined magnitude is recorded within the lacustrine highstand deposits of the last lake about 300 years ago there is no evidence of earlier faulting events in sediments that possibly may correlate to the penultimate lake approximately 550 years b p below an unconformity 4000 year old deltaic deposits are intensely faulted by previous slip along the imperial fault these data suggest that the slip rate on the imperial fault for the past 300 550 years is only about 15 20 mm yr substantially less than that expected from geodetic measurements and regional structural models this in turn suggests that either slip is accommodated by other faults in the border region or that strain release on the imperial fault is characterized by episodic clustered behavior

numerical simulation of spontaneous rupture processes on twonon coplanar faults the effect of geometry on fault interaction summary analyses of earthquake sources have revealed that the earthquake rupture process is complex and that the rupture does not occur on a single plane earthquake faults are often composed of several subfaults and rupture propagation tends to decelerate or terminate at places where the fault strike changes these observations imply that fault geometry including fault steps and fault strike change plays an important role in earthquake rupture complexity in this paper we calculate the spontaneous rupture processes of two non coplanar faults in 2 d in plane problems attempting to clarify the eiect of fault geometry we consider two simple modelsmodels in which two faults are either parallel or perpendicular to each other we calculate spontaneous rupture propagation on the faults bya nite diierence method andwe then compare the results in our simulations rupture initially grows on the main fault and stress perturbation from the main rupture then triggers rupture on the secondary fault propagation of the main fault rupture controls a spatio temporal pattern ofstress diierence in the uniform elastic medium which determines the rupture process of the secondary fault the rupture propagation and termination of the secondary fault are signi cantly diierent between the two models the diierence is obvious when rupture of the main fault is arrested and the secondary fault is located near the arrested end of the main fault when the secondary fault is parallel to the main fault rupture can propagate ahead on the secondary fault however when the secondary fault is perpendicular to the main fault rupture is either not triggered on the secondary fault or soon terminates if triggered this variation of the rupture process implies that fault interaction depending on geometry can explain the termination and change of rupture at places where the fault strike varies this shows the importance of the fault geometry in studying spontaneous dynamic rupture processes

large scale tin depletion in the tanjungpandan tin granite belitung island indonesia the middle triassic tanjungpandan batholith on belitung island is associated with major alluvial tin ore deposits the batholith consists of two petrogenetically different ilmeniteseries rock suites an areally dominating biotite granite suite and a quartz syenite suite of more restricted extent the granite suite has a low pressure minimum melt composition the syenite suite covers a large compositional field from gabbroic cumulate rocks to alkali feldspar granite pegmatite both rock suites show extended fractional crystallization trends trace element patterns are partially disturbed by fluid interaction extremely low tin contents mean sn concentrations 2 4 ppm seem to be related to hydrothermal removal of tin by high temperature low f sub o 2 fluids the unusually low fe super 3 fe super 2 ratios of the granitic rocks allowed an exceptional degree of hydrothermal redistribution of tin the tin distribution pattern clearly distinguishes the tanjungpandan situation and that of neighboring tin granites of the tin islands from other major tin granite suites in the world

petrogenesis of malaysian granitoids in the southeast asian tin belt part 2 u pb zircon geochronology and tectonic model in our complementary geochemical study part 1 the malaysian granitoids of the southeast asian tin belt were divided into a middle permian to late triassic i type dominated eastern province indochina terrane and a triassic to early jurassic transitional i s type main range province sibumasu terrane separated by the bentong raub suture zone which closed in the late triassic previous geochronology has relied on only a few u pb zircon ages together with k ar and whole rock rb sr ages that may not accurately record true magmatic ages we pre sent 39 new high precision u pb zircon ion microprobe ages from granitoids and vol canics across the malay peninsula our results show that ages from the eastern province granitoids span 289 220 ma with those from the main range province granitoids being entirely late triassic spanning 227 201 ma a general westerly younging magmatic trend across the malay peninsula is considered to refl ect steepening and roll back of the bentong raub subduction zone during progressive closure of paleo tethys the youngest ages of subduction related granites in the eastern province roughly coincide with the youngest ages of marine sedimentary rocks along the paleo tethyan suture zone our petrogenetic and u pb zircon age data support models that relate the eastern province granites to pre collisional andean type magmatism and the western main range province granites to syn and post collisional crustal melting of sibumasu crust during the late triassic tin mineralization was mainly associated with the latter phase of magmatism two alternative tectonic models are discussed to explain the triassic evolution of the malay peninsula the fi rst involves a second late triassic to jurassic or early cretaceous east dipping subduction zone west of sibumasu where subduction related hornblende and biotite bearing granites along sibumasu are paired with main range crustal melt tinbearing granites analogous to the bolivia cordilleran tin bearing granite belt the second model involves westward underthrusting of indochina beneath the west malaya main range province resulting in crustal thickening and formation of tin bearing granites of the main ranges cretaceous granitoids are also present locally in singapore ubin diorite on tioman island in the noring pluton of the stong complex eastern province and along the sibumasu terrane in southwest thailand and burma myanmar refl ecting localized crustal melting

source parameters and tectonic origin of the 1996 june 1 tianzhu mw 5 2 and 1995 july 21 yongden mw 5 6 earthquakes near the haiyuan fault gansu china summary the 1996 june 1 tianzhu mw 5 2 ms 4 9 and the 1995 july 21 yongden mw 5 6 ms 5 4 earthquakes are the two largest events recorded in the last 10 years between the 1990 october 20 ms 5 8 and the recent 2000 june 6 ms 5 6 earthquakes near the tianzhu seismic gap on the haiyuan fault in northeastern tibet we use frequency time analysis ftan to extract the fundamental modes of love and rayleigh waves from digital records a joint inversion of their amplitude spectra and of p wave first motion polarities is then performed to calculate the source parameters focal mechanisms depths and seismic moments of these two ms 5 earthquakes such a joint inversion is tested for the first time we use iris and geoscope network records for period ranges of 20 40 s for the former event and 35 70 s for the latter the inversion of the tianzhu earthquake yields nodal planes with strike dip and slip of 282 72 and 3 and 191 87 and 162 respectively a focal depth around 12 km and a seismic moment of 0 56 1017 n m consistent with the harvard cmt calculation and the alignment and depths of the aftershocks recorded by a local network we propose two possible tectonic interpretations for this off fault event the solution for the yongden earthquake is consistent with a thrust with strike dip and slip of 105 45 and 75 respectively a focal depth around 6 km and a seismic moment of 2 4 1017 n m also in agreement with the harvard cmt mechanism the distribution of the aftershocks recorded by a regional network and the general tectonic setting that we refine

slip on the elmore ranch fault during the past 330 years and its relation to slip on the superstition hills fault abstract the elmore ranch fault is a left lateral fault that strikes northeast within the right lateral transform boundary that strikes northwest through southern california it lies transverse and adjacent to the segment of the superstition hills fault that ruptured in 1987 rupture of the elmore ranch fault m s 6 2 preceded rupture of the superstition hills fault m s 6 6 by about 11 4 hr the elmore ranch fault slipped at the surface in 1987 with left lateral displacements of up to 130 mm geological data indicate that it had slipped prehistorically sometime after about 1660 a d probably in a single event excavations at three sites enable the following comparisons at these sites the only significant component of dip slip down to the southeast was found on the west strand for slip previous to 1987 the superstition hills fault has also been documented to have experienced one slip event between 1660 and 1987 thus these slip events on the elmore ranch and superstition hills faults may have occurred in a sequence similar to that in 1987 neither the main fault nor the cross fault however appear to have exactly duplicated their previous surficial slip previous slip was probably smaller on the superstition hills fault and larger on the elmore ranch fault zone than in the 1987 event because the temporal correlation between previous slip events is not proven rupture sequences other than a doublet in which main fault rupture follows cross fault rupture are possible

new slip along parts of the 1968 coyote creek fault rupture california on 28 and 30 november 1987 we found new surface ruptures along the central break of the coyote creek fault s 1968 rupture mapped slip that may have been triggered by the superstition hills earthquakes of 24 november 1987 was dominantly right lateral and ranged up to 15 mm total length of the new ruptures was about 3 km distributed along two quasi continuous segments of the main fault plus one segment of a secondary fault all of which ruptured in 1968 the longest segment of new rupture followed the northeast side of the ocotillo badlands for 2 3 km newly mapped slip in 1987 occurred along parts of the coyote creek fault that were characterized in 1968 by several features these were large total dextral slip a prominent vertical slip component rupture along single fractures instead of en echelon cracks and large afterslip in the few years following the 1968 earthquake past episodes of triggered slip on the san andreas imperial and superstition hills faults were hypothesized by others to be precursory phenomena the 1987 slip on the coyote creek fault however may be an episode of afterslip this suggestion is supported by the decrease in creep rates since 1968 shown by data from two alinement arrays on the coyote creek fault the correct interpretation of triggered slip events and their value as earthquake precursors therefore depends upon a good knowledge of the slip history of a fault

phanerozoic plate boundaries in mainland se asia the himalayas and tibet recently available geological data on tibet yunnan and burma facilitate recognition of phanerozoic subduction systems and two continental fragments of gondwanaland which extend through mainland se asia a cambrian subduction system and 5 mesozoic early caenozoic collision belts are identified in the region indochina eastern thailand and central tibet accreted to china in the early triassic western se asia and s tibet separated from gondwanaland in the permian or early triassic and collided with asia in the late triassic and the western burma island arc system collided with asia in the jurassic upper triassic flysch and schist in the eastern indoburman ranges were accreted to western burma in the jurassic early cretaceous during eastward subduction and formation of a back arc thrust belt following collision of greater india with arc complexes to the n in the cretaceous and with tibet in the early eocene western burma moved northwards about 450 km along the sagaing namyin ridge thrust transform fault formation of the 3 major belts of tin granites and the porphyry copper deposits in the region took place in specific tectonic settings within the subduction systems and collision belts

tracing magma mixing in granite genesis in situ u pb dating and hf isotope analysis of zircons in situ zircon u pb and hf isotopic data have been determined for mafic microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china in order to constrain the sources and petrogenesis of granites the zircon u pb age of the enclaves 120 1 ma is identical to that of the host monzogranite 120 1 ma establishing that the mafic and felsic magmas were coeval the hf isotopic composition of the enclaves ehf t 4 5 to 6 2 is distinct from the host monzogranite ehf t 15 1 to 25 4 indicating that both depleted mantle and crustal sources contributed to their origin the depleted mantle component was not previously revealed by geochemical and nd and sr isotopic studies showing that zircon hf isotopic data can be a powerful geochemical tracer with the potential to provide unique petrogenetic information some wall rock contamination is indicated by inherited zircons with considerably older u pb ages and low initial hf isotopic compositions hafnium isotopic variations in early cretaceous zircons rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead mixing of mantle derived mafic magmas with crustal derived felsic magmas coupled with assimilation of wall rocks is compatible with the data

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

the chanthaburi terrane of southeastern thailand stratigraphic confirmation as a disrupted segment of the sukhothai arc a permo triassic volcanic arc system the sukhothai arc is recognised between the indochina and sibumasu continental blocks the chanthaburi terrane is here interpreted as a fault detached highly disrupted southern segment of the sukhothai arc occupying part of southeastern thailand and extending into cambodia the klaeng tectonic line is defined as the boundary between the chanthaburi terrane and sibumasu block the stratigraphy of the chanthaburi terrane is compared with that of the sukhothai terrane in northern thailand the late palaeozoic mesozoic sequences of these two volcanic arc terranes in the sukhothai zone share important similarities but show marked contrasts to those of the sibumasu and indochina blocks where the late permian triassic is largely absent due to the indosinian i unconformity western indochina or is dominantly carbonates with little terrigenous clastic input sibumasu there is no clear evidence of pre carboniferous sedimentary rocks for either the sukhothai or chanthaburi terranes late permian lyttoniid brachiopod shale near klaeng in the chanthaburi terrane was revisited the brachiopod previously reported as leptodus is re identified to oldhamina the genus previously known elsewhere in southeast asia only in the huai tak formation of the sukhothai terrane oldhamina in thailand is confined to the sukhothai arc the marine stratigraphy of the sukhothai arc is represented by a permian triassic lithological succession of mixed carbonates and siliciclastics with common volcanic material the late permian and triassic litho and biostratigraphy of the chanthaburi terrane are comparable with the upper ngao and lampang groups of the sukhothai terrane in particular they share similar successions from oldhamina brachiopod bearing shale to palaeofusulina colaniella foraminifer bearing limestone in the latest permian marine depositional conditions were terminated on the sukhothai arc by end triassic times later than on the indochina block late permian but earlier than on the sibumasu block jurassic cretaceous

maximum and minimum water contents of granitic melts generated in the crust a reevaluation and implications abstract recent results of studies aimed to determine the water solubilities and the liquidus temperatures in synthetic and natural granitic systems are used to constrain the minimum water contents of granitic melts generated in the crust as a function of pressure temperature melt composition and water activity it is concluded that melts generated in the crust at high temperature and low water activities such as a type granites contain higher water contents than previously assumed up to 20 at 800 900 c and 3 7 kbar as a consequence the melt fraction produced at a given amount of available water can be up to 20 lower the minimum water content of melts generated by partial melting of crustal protoliths especially quartzofeldspathic rocks can be predicted adequately from the liquidus curves in granitic systems this water content can be higher if the melt composition departs from a minimum or eutectic quartzofeldspathic composition melts generated from quartzofeldspathic rocks at low temperature 750 c and below are necessarily water rich 5 wt h 2 o and have approximately the same viscosity or even slightly lower viscosities than melts generated at higher temperatures viscosities in the range 10 4 3 10 5 4 pa s recent experimental data also show that the value of the positive d p d t slope of the liquidus curves for fixed water contents above 800 c is lower than predicted by previous models thus adiabatic decompression produces a higher amount of melt than previously assumed at high temperature the formation of melt by adiabatic decompression can be up to 50 higher than assumed

late quaternary slip rate gradient defined using high resolution topography and 10be dating of offset landforms on the southern san jacinto fault zone california 1 recent studies suggest the san jacinto fault zone may be the dominant structure accommodating pa na relative plate motion however because the late quaternary slip history of the southern san andreas fault system is insufficiently understood it is difficult to evaluate the partitioning of deformation across the plate boundary and its evolution landforms displaced by the clark fault of the southern san jacinto fault zone were mapped using high resolution airborne laser swath topography and selected offset landforms were dated using cosmogenic 10be beheaded channels at rockhouse canyon displaced by 500 70 m and 220 70 m have been dated to 47 8 ka and 28 9 ka respectively farther south near the southern santa rosa mountains an alluvial deposit displaced by 51 9 m has been dated to 35 7 ka from these sites the slip rate of the clark fault is determined to diminish southward from 8 9 2 0 to 1 5 0 4 mm yr this implies a slip rate decrease along the clark fault from anza southeastward to its surface termination near the salton trough where slip is transferred to the coyote creek fault and additional deformation is compensated by folding and thrusting in the basin these data suggest that since 30 to 50 ka the slip rate along the southern san jacinto fault zone has been lower than or equivalent to the rate along the southernmost san andreas fault accordingly either the slip rate of the san jacinto fault has substantially decreased since fault initiation or fault slip began earlier than previously suggested

zircon u pb ages in myanmar magmatic metamorphic events and the closure of a neo tethys ocean abstract previous isotopic age studies have concluded that the main metamorphism in the mogok metamorphic belt mmb in myanmar was tertiary and caused by collision with or underthrusting by india we present here results of zircon u pb age determinations on 18 samples from myanmar largely on intrusive rocks from the north trending 550 km long shan scarps segment of the sickle shaped mmb the oldest determination is 491 ma on orthogneiss north of mandalay interpreted as a protolith age and similar to the stratigraphic age of the bawdwin volcanics augen gneiss at kyaukse has a 114 ma protolith age our zircon u pb ages on undeformed intrusive rocks in the mmb range from cretaceous to miocene the oldest 128 ma on a diorite near yebokson implies an earliest cretaceous minimum age for regional metamorphism here younger ages on undeformed intrusions include 91 ma on diorite at mokpalin 72 ma on the weakly foliated garnet bearing nattaung granite 44 and 48 ma respectively on the mec and sedo granites and 17 20 ma on granite dykes for the 128 ma diorite sr and nd isotopes indicative of a continental crust component and mapped continuity of metamorphic host rocks suggest correlation with mid early cretaceous plutons in the eastern transhimalayas zircon u pb ages for the mec sedo and other granites within the mmb and slate belt help to define a late cretaceous to early eocene age range for mostly ilmenite series peraluminous granites within the western granite belt and more restricted western tin belt of myanmar and southern thailand in the wuntho popa arc west of the dextral sagaing fault our new u pb zircon age of 105 ma on diorite at salingyi supports previous k ar ages 106 93 ma for pre tertiary intrusions in the cretaceous this arc may have occupied the andaman sea and continued northwards through the mokpalin diorites and west of the mmb to the 103 80 ma i type plutons in the gandise batholith of southern tibet we interpret the mmb and slate belt as part of a western myanmar block separated in the jurassic from the shan plateau to the east by the southwestward continuation of the bangong nujiang luxi neo tethys i ocean we relate most intrusive and metamorphic events in and near the mmb to westward subduction of this ocean and end jurassic collision of the plateau with the overriding western myanmar slate belt block to orogenic polarity reversal and early cretaceous westward translation of the plateau sequence over the suture zone and to eastward subduction of the ancestral indian ocean or neo tethys ii beneath myanmar with generation of the wuntho popa arc beginning before the late cretaceous the mmb includes meta plateau rocks near mandalay but meta slate belt rocks to the north and south within the mmb previous monazite xenotime thorite ages of eocene oligocene and oligocene early miocene cooling ages on micas with no deformation in eocene granites suggest a high temperature thermal event related to intrusion of these and other granites during a previously proposed regional extension our data imply that the main fabric forming metamorphic event in the mmb pre dated the india asia collision

slip along the superstition hills fault associated with the 24 november 1987 superstition hills california earthquake surficial slip along the entire mapped length of the superstition hills fault in southern california occurred in association with the superstition hills earthquake m s 6 6 of 24 november 1987 we made repeated measurements of surface slip at 36 sites along the fault and occupied 64 sites at least once at our sites dextral slip was as high as 48 5 cm 1 day after the earthquake and 71 cm 2 months after the measurements show that slip during the period from hr to several hundred hr following the event is described by a simple power law of time extrapolation to t 1 min indicates that co seismic slippage ranged from 5 to 23 cm at 10 of our best recorded sites suggesting that finite co seismic slippage occurred along the length of the fault these extrapolations are supported by a measurement made at imler road 30 min after the shock measurements are complete through october 1988 at many sites the form of slip rate was decay changed from power law to a function of log time during the interval between 300 and 500 hr after the earthquake logarithmic slip rate decay in time was observed for a period of several yr after the parkfield borrego mountain and imperial valley earthquakes those measurements may have begun too late to resolve power law behavior at early times if current logarithmic behavior of the superstition hills fault persists right lateral slippage will approach 90 cm 10 yr after the rupture changes in the along fault displacement profile correlate well with geometric features including a fault bend and a major fault step moreover slip behavior appears to be correlated to the thickness of sedimentary cover along the fault also the northern half of the fault is bounded by a large block of continental crystalline basement the presence of this block may have contributed to the relatively uniform early slip behavior observed there

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented

behavior of the superstition hills fault during the past 330 years we have investigated the recent prehistoric behavior of the superstition hills fault by examining its effect on the beach deposits of ancient lake cahuilla excavation of these sediments in three dimensions where they are cut by the fault has enabled determination of total offset since the latest highstand of the lake about 330 years ago as of 3 march 1988 total dextral offset was 1106 50 mm about 609 mm of this amount can be attributed to one or more slip events before 1987 the remaining slip occurred during the moderate earthquake of 24 november 1987 and as subsequent aftercreep additional aftercreep here might produce a total of 1210 100 mm for that event thus if afterslip continues according to our prediction slip associated with the penultimate seismic slip event on the superstition hills fault was only about half of the co seismic slip and predicted afterslip associated with the 1987 earthquake this difference established at a single site on the fault may reflect a larger size for the 1987 event than for its predecessor we calculate that the slip rate of the superstition hills fault zone averaged over the past 330 years is between about 2 and at least 6 mm yr at this site during this time the average interval between large surface slip events on the superstition hills fault has been between about 150 and 300 years the pre 1987 slip event documented in our excavations could have occurred at any time between a d 1660 and about a d 1915 these results are significant for understanding earthquake recurrence and patterns of earthquakes in the imperial and coachella valleys

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

surface faulting along the superstition hills fault zone and nearby faults associated with the earthquakes of 24 november 1987 the m 6 2 elmore desert ranch earthquake of 24 november 1987 was associated spatially and probably temporally with left lateral surface rupture on many northeast trending faults in and near the superstition hills in western imperial valley three curving discontinuous principal zones of rupture among these breaks extended northeastward from near the superstition hills fault zone as far as 9 km the maximum observed surface slip 12 5 cm was on the northern of the three the elmore ranch fault at a point near the epicenter twelve hours after the elmore ranch earthquake the m 6 6 superstition hills earthquake occurred near the northwest end of the right lateral superstition hills fault zone surface rupture associated with the second event occurred along three strands of the zone here named north and south strands of the superstition hills fault and the wienert fault for 27 km southeastward from the epicenter in contrast to the left lateral faulting which remained unchanged throughout the period of investigation the right lateral movement on the superstition hills fault zone continued to increase with time a behavior that was similar to other recent historical surface ruptures on northwest trending faults in the imperial valley region we measured displacements over 339 days at as many as 296 sites along the superstition hills fault zone and repeated measurements at 49 sites provided sufficient data to fit with a simple power law data for each of the 49 sites were used to compute longitudinal displacement profiles for 1 day and to estimate the final displacement that measured slips will approach asymptotically several years after the earthquakes the maximum right lateral slip at 1 day was about 50 cm near the south central part of the north strand of superstition hills fault and the predicted maximum final displacement is probably about 112 cm at imler road near the center of the south strand of the superstition hills fault the overall distributions of right lateral displacement at 1 day and the estimated final slip are nearly symmetrical about the midpoint of the surface rupture the average estimated final right lateral slip for the superstition hills fault zone is about 54 cm the average left lateral slip for the conjugate faults trending northeastward is about 23 cm the southernmost ruptured member of the superstition hills fault zone newly named the wienert fault extends the known length of the zone by about 4 km the southern half of this fault south of new river expressed only vertical displacement on a sinuous trace the maximum vertical slip by the end of the observation period there was about 25 cm but its growth had not ceased photolineaments southeast of the end of new surface rupture suggest continuation of the superstition hills fault zone in farmland toward mexico

granitic magmatism basement ages and provenance indicators in the malay peninsula insights from detrital zircon u pb and hf isotope data abstract the malay peninsula lies on two continental blocks sibumasu and east malaya which are intruded by granitoids in two provinces the main range and eastern previous models propose that permian triassic granitoids are subduction related and syn to post collisional we present 752 u pb analyses that were carried out on zircons from river sands in the malay peninsula of these 243 grains were selected for hf isotope analyses our data suggest a more complex sibumasu east malaya collision history 176hf 177hfi ratios reveal that permian triassic zircons were sourced from three magmatic suites a permian crustally derived granitoids b early middle triassic granitoids with mixed mantle crust sources and c late triassic crustally derived granitoids this suggests three permian triassic episodes of magmatism in the malay peninsula two of which occurred in the eastern province although the exact timing of the sibumasu east malaya collision remains unresolved current data suggest that it occurred before the late triassic probably in late permian early triassic our data also indicate that sibumasu and east malaya basements are chronologically heterogeneous but predominantly of proterozoic age some basement may be neoarchaean but there is no evidence for basement older than 2 8 ga finally we show that hf isotope signatures of triassic zircons can be used as provenance indicators

tectonic evolution of the sibumasu indochina terrane collision zone in thailand and malaysia constraints from new u pb zircon chronology of se asian tin granitoids three principal granite provinces are defined across se asia as follows 1 the western thailand myanmar burma province consists of hornblende biotite i type granodiorite granites and felsic biotite k feldspar garnet tourmaline granites associated with abundant tin mineralization in greisen type veins new ion microprobe u pb dating results from phuket island show zircon core ages of 212 2 and 214 2 ma and a thermal overprint with rims of 81 2 1 2 and 85 75 ma 2 the north thailand west malaya main range province has mainly s type biotite granites and abundant tin mineralization resulting from crustal thickening following collision of the sibumasu plate with indochina during the mid triassic biotite granites around kuala lumpur contain extremely u rich zircons up to 38000 ppm that yield ages of 215 7 and 210 7 ma 3 the east malaya province consists of dominantly permian triassic i type hornblende biotite granites but with subordinate s type plutons and a type syenite gabbros biotite k feldspar granites from tioman island off the east coast of malaysia also yield a zircon age of 80 1 ma showing cretaceous magmatism in common with province 1 geological and u pb geochronological data suggest that two east dipping in present day coordinates subduction zones are required during the triassic one along the bentong raub palaeo tethyan suture and the other west of the phuket burma province 1 belt supplementary material a full description of u pb analytical methods used and data tables are available at www geolsoc org uk sup18523

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts

timing and slip for prehistoric earthquakes on the superstition mountain fault imperial valley southern california trenches excavated across the superstition mountain fault in the imperial valley california have exposed evidence for four prehistorical earthquakes preserved in displaced lacustrine stratigraphy associated with ancient lake cahuilla the presence of shoreline peat accumulations along with abundant detrital charcoal allows for high precision age determination of some stratigraphic units thereby providing constraints on the timing of three of the paleoearthquakes these three events occurred within a 480 to 820 year interval during the past 1200 years the most recent earthquake event 1 occurred during a fluvial phase of deposition between a d 1440 1637 immediately prior to the inundation of the cahuilla basin at about a d 1480 and 1660 a channel margin was offset 2 2 0 4 0 15 m in this rupture suggesting an earthquake with a magnitude 7 the penultimate event event 2 also occurred during fluvial deposition after a d 1280 but before another lakestand at a d 1440 1640 lateral slip could not be resolved for event 2 however based on juxtaposition of dissimilar units and the amount of deformation produced by this event it is presumed that this was also a large earthquake the timing of event 3 is constrained to have occurred between about a d 820 and 1280 this event is represented by several fractures and small displacements that rupture up to a distinct stratigraphic level or event horizon slip was not resolved for this event finally the timing of event 4 is very poorly constrained to between a d 964 and 4670 b c undoubtedly many events may have occurred during this period notably the past three earthquakes occurred within a period of less than 820 years and it has been over 350 years since the last earthquake

granite related tin metallogenic events and key controlling factors in peninsular malaysia southeast asia new insights from cassiterite u pb dating and zircon geochemistry