triggered surface slips in the salton trough associated with the 1999 hector mine california earthquake surface fracturing occurred along the southern san andreas superstition hills and imperial faults in association with the 16 october 1999 mw 7 1 hector mine earthquake making this at least the eighth time in the past 31 years that a regional earthquake has triggered slip along faults in the salton trough fractures associated with the event formed discontinuous breaks over a 39 km long stretch of the san andreas fault from the mecca hills southeastward to salt creek and durmid hill a distance from the epicenter of 107 to 139 km sense of slip was right lateral only locally was there a minor 1 mm vertical component of slip dextral slip ranged from 1 to 13 mm maximum slip values in 1999 and earlier triggered slips are most common in the central mecca hills field evidence indicates a transient opening as the hector mine seismic waves passed the southern san andreas fault comparison of nearby strong motion records indicates several periods of relative opening with passage of the hector mine seismic wave a similar process may have contributed to the field evidence of a transient opening slip on the superstition hills fault extended at least 9 km at a distance from the hector mine epicenter of about 188 to 196 km this length of slip is a minimum value because we saw fresh surface breakage extending farther northwest than our measurement sites sense of slip was right lateral locally there was a minor 1 mm vertical component of slip dextral slip ranged from 1 to 18 mm with the largest amounts found distributed or skewed away from the hector mine earthquake source slip triggered on the superstition hills fault commonly is skewed away from the earthquake source most notably in 1968 1979 and 1999 surface slip on the imperial fault and within the imperial valley extended about 22 km representing a distance from the hector mine epicenter of about 204 to 226 km sense of slip dominantly was right lateral the right lateral component of slip ranged from 1 to 19 mm locally there was a minor 1 2 mm vertical component of slip larger proportions of vertical slip up to 10 mm occurred in mesquite basin where scarps indicate long term oblique slip motion for this part of the imperial fault slip triggered on the imperial fault appears randomly distributed relative to location along the fault and source direction multiple surface slips both primary and triggered slip indicate that slip repeatedly is small at locations of structural complexity

holocene rate of slip and tentative recurrence interval for large earthquakes on the san andreas fault cajon pass southern california abstract detailed mapping of the san andreas fault zone where it crosses cajon creek southern california has revealed a number of late quaternary deposits and geomorphological features offset by the fault radiocarbon dates from alluvial and swamp deposits provide a detailed chronology with which to characterize the activity of the san andreas fault four independent determinations of the slip rate on the san andreas fault yield an average rate of 24 5 3 5 mm yr for the past 14 400 years the similarity of the four values which span different intervals of time from 5900 to 14 400 years ago suggest that the slip rate has been constant during this period the slip rate confirms that the san andreas fault is accumulating slip faster than any other fault in the plate boundary throughout california also the sum of the slip rates on the san andreas 24 5 mm yr and the san jacinto 10 mm yr faults south of their junction is the same as the san andreas north of their junction 35 mm yr an excavation provided evidence for at least two and up to four earthquakes that caused rupture on the fault between 1290 and 1805 a d and tentative evidence for six earthquakes in about the last 1000 years both lines of evidence imply an average recurrence interval for large earthquakes of about 1 to 2 centuries combined with the historic record this investigation indicates that the last major earthquake at cajon creek was probably at the beginning or middle of the 18th century while the record at cajon creek may suggest that the next major earthquake on the san andreas fault is overdue the data can be interpreted to indicate that the recurrence interval for earthquakes on the san andreas south of the 1857 rupture is 3 to 4 centuries and that the anticipated event should not be expected until the next century

behavior of the southernmost san andreas fault during the past 300 years surficial creep occurs at low rates along the coachella valley segment of the san andreas fault which has not produced a large earthquake during the period of historical record geodetic data indicate however that the crust adjacent to this segment of the san andreas fault is accumulating strain at a high rate furthermore neotectonic and paleoseismic data indicate that the fault does produce very large earthquakes every two to three centuries in view of its long term behavior the occurrence of creep along the surficial trace of the fault in the coachella valley is of particular interest along two short reaches of the san andreas fault in the coachella valley measurements of offset geological deposits and man made structures and from alignment arrays and creep meters show that slip rates of 2 4 mm yr near indio and near the salton sea have persisted for the past three centuries this slow aseismic surficial creep is not a transient precursor to seismic failure of this segment of the fault we suggest that the coachella valley segment of the san andreas fault creeps in its upper few kilometers this behavior may be due to tectonically induced high pore pressures in the coarse sediments that abut the fault

stressing of locked patches along a creeping fault an analysis is presented of the stressing of locked patches along a fault zone which is creeping elsewhere the model consists of strike slip faulted elastic lithospheric plates loaded in a manner equivalent to imposition of a remotely uniform tectonic shear stress the fault zone has an inhomogeneous strength distribution both depth wise and along strike it is modeled as being composed of locked patches and freely slipping parts treated as cracks the solution is given with the use of the line spring model which analyzes the problem by thickness averaged plane stress theory for lithospheric plates which slip along a discontinuity cut at the plate boundary as a boundary condition thickness averaged stress and slip at each local section along the cut was related to one another by the result of an antiplane strain analysis of slip for the crack or crack pair which describes the slipping and locked depth ranges at that section the analysis indicates that the slip distribution along creeping parts of the fault as well as the stress distribution along locked patches depends strongly on the geometry of these zones the model is used to examine stress concentrations associated with a slip deficient seismic gap along strike and to study the effect of local irregularities in the margin of a locked region it is also used to simulate slip and stressing processes associated with the creeping portion of the san andreas fault in central california between the presently locked zones of the great 1906 and 1857 ruptures and to constrain the nature of an apparently locked zone at the southeastern end which ruptures in characteristic parkfield earthquakes near fault creep and broadscale displacement data along the fault since the 1966 parkfield earthquake and inferences from seismicity distributions are used limitations of the modeling procedure at short spatial wavelengths prohibit an accurate description of the parkfield locked patch but results suggest that it may be localized and occupy a small fraction of area of the normal seismogenic zone an effective remote stressing rate of order 0 3 10 6 shear modulus yr is inferred together with a less well constrained 30 to 40 km lithospheric thickness for consistency with the displacement data results enable estimates of stress accumulation along the locked 1857 rupture zone and the build up of fracture energy release capability of order 107 j m2 in 150 yr at its lower margin

petrogenesis of late mesozoic high ba sr granites in the qiushuwan cumo orefield implications for the distribution of porphyry mo mineralization in the east qinling area of central china abstract the qinling dabie orogenic belt of china is well known for its large mo resources there have been many studies of the genesis of the mo deposits but the reasons for the intensive mineralization during the late mesozoic and the spatially uneven distribution of the resulting ore deposits are not fully understood deposits with reserves of 6 mt of mo occur predominantly in the southern margin of the north china craton ncc and are mostly late mesozoic porphyry deposits in comparison a few relatively insignificant and cu dominated porphyry ore deposits have been identified in the north and south qinling terranes this study presents new whole rock geochemical isotopic and zircon u pb age data for ore bearing granites associated with the qiushuwan cu mo deposit the largest porphyry deposit in the north qinling nq terrane which provide insights into the asymmetric distribution of mo mineralization in this region the rocks display high k calc alkaline to shoshonitic affinities and are metaluminous to weakly peraluminous with high ba and sr contents low rb nb and ta contents and depletion in heavy rare earth elements and y which are features typical of high ba sr granites zircon u pb dating indicates that the granites crystallized at ca 145 ma their narrow ranges of whole rock initial 87sr 86sr ratios 0 7056 0 7069 and end t 7 4 to 9 7 zircon ehf t 2 49 to 5 13 and 18o 5 58 to 6 49 values together with the presence of significant nd hf isotopic decoupling hf 7 61 to 11 3 indicate that the parent magma was derived from partial melting of enriched subcontinental lithospheric mantle with minor assimilation of the lower crust in contrast late mesozoic granitic rocks in the southern margin of the ncc including both mineralized and barren intrusions are geochemically associated with the crust of the northern margin of the yangtze block yb the yb contains mo rich shales that are thought to have been subducted beneath the southern margin of the ncc during the triassic melting of these mo rich black shales would have mobilized mo a process that enabled the formation of the extensive mo mineralization associated with the late mesozoic granites of the southern margin of the ncc this indicates that the extensive mo mineralization within the southern margin of the ncc is genetically related to a mo rich source that was generated by the stagnation of subducted yb continental crust beneath the southern margin of the ncc in comparison the less significant mo mineralization within the east qinling orogenic belt might reflect the variable removal of the subducted yb continental slab during post collisional intracontinental orogenesis

phanerozoic sanukitoids from caledonian scotland implications for archean subduction sanukitoids represent a volumetrically minor but important series of neoarchean granitoids enriched in large ion lithophile elements e g ba sr and light rare earth elements and with relatively high compatible elements e g mg ni and cr petrogenetic models have favored an origin in the suprasubduction mantle wedge so their sudden appearance ca 2 95 2 68 ga has made them central to the ongoing debate about the beginnings of modern plate tectonics caledonian high ba sr granites from the northern highlands of scotland are petrological and compositional equivalents the caledonian examples have not undergone subsequent reworking and their petrogenetic setting can be used to inform genetic models for sanukitoids prolonged subduction preceded emplacement of the high ba sr granites in a short interval 10 ma at the end of the caledonian orogeny sediment subduction was responsible for elemental and isotopic enrichments and slab breakoff triggered melting in the subcontinental lithospheric mantle this implies that during the neoarchean the evolving tectonothermal regime moved the locus of melting from the basaltic slab to the sediment infused mantle wedge creating the first subcontinental lithospheric mantle sanukitoids may then have resulted from widespread closely subsequent slab breakoff events producing evolved magmas by familiar fractionation mechanisms careful study of secular variations in high ba sr magmas could constrain the evolution of the subcontinental lithosphere

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

petrogenetic constraints for the genesis of archaean sanukitoid suites geochemistry and isotopic evidence from karelia baltic shield new sm nd isotope data are presented for late archaean sanukitoid suites of the karelian granite greenstone terrane of the baltic shield within the terrane there are regional variations in the nd isotope compositions of the sanukitoids sanukitoids in the youngest central karelian domain have nd isotope characteristics similar to depleted mantle whereas those from the older west karelian and vodlozero domains have lower initial end values the isotopic heterogeneity of the sanukitoids is interpreted to result from variations in the time interval between mantle source enrichment and the partial melting that produced the sanukitoid magmas we therefore suggest a two stage model of the generation of sanukitoid magmas during first stage the mantle was metasomatised by fluids and or melts generated during subduction or tectonic underplating later between 2 74 and 2 70 ga a tectonothermal anomaly generated the sanukitoid magmas by melting of the previously metasomatised mantle most of the sanukitoid intrusions are cut by calc alkaline lamprophyre dykes that have the similar geochemical signatures to their sanukitoid wall rocks new sm nd isotope data for these lamprophyres suggest a genetic kinship between the sanukitoids and the lamprophyres comparison between chemical signatures of sanukitoids and modern subduction related magmas shows that archaean sanukitoids actually have no modern analogues sanukitoid melts can be modelled as partial melts of mantle that had been metasomatised a short time previously the melts could have been in equilibrium with residues containing ol cpx plus minor phl and grt at a pressure of about 2 5 gpa and a temperature of 1150 1230 8c the small percentage of residual phlogopite would retain rb in the mantle and explain the peculiar signature of low rb and high ba and sr characteristic of the sanukitoids we envisage a temporal evolution of the composition of the mantle in this region this pattern of evolution controlled production of the sanukitoid melts and explains why the sanukitoids have such a restricted range of ages sanukitoid magma production must have followed from a major global mantle enrichment event these magmas could not have been produced earlier because the archaean mantle had not become sufficiently enriched before 2 7 ga we suggest that their scarcity after the major period of sanukitoid magmatism may be due to the increased thickness of overlying crust which can inhibit mantle enrichment

reconstruction of late pleistocene paleoenvironments in southern germany using two high resolution loess paleosol records abstract two loess paleosol sequences from the heilbronn basin in southwestern germany frankenbach and talheim have been investigated to gain information about environmental conditions during the last interglacial glacial cycle since paleoenvironmental research on terrestrial archives is crucial for a better understanding of past climatic and environmental conditions the profiles were studied using a multi proxy approach applied methods include the analyses of grain size distribution element contents sediment color rock magnetism micromorphology and black carbon bc via benzene polycarboxylic acids bpca the data reveal that the two profiles show large variations in conservation due to their different geomorphologic positions moreover the results imply a subarctic climate with stable conditions during the middle pleniglacial mis 3 in situ soil formation phase while the lower pleniglacial mis 4 was characterized by erosion and reworking of eemian and early glacial mis 5 material but also by accumulation of aeolian material during the late lower pleniglacial mis 4 in frankenbach the results further suggest that the rhine river floodplain has been a major source for the accumulated material in the two profiles which indicates westerly wind directions during the time of accumulation the low gsi and u ratio of upper pleniglacial mis 2 sediments supported by the overall high content of fine material imply a larger distance to the source area we give an overview of loess in the heilbronn basin and place it in a wider context of loess in western europe

geochemical and numerical constraints on neoarchean plate tectonics this paper discusses early neoarchean 2 8 2 7 ga plate tectonics by integrating knowledge from new geochemical observations and numerical models based on a geochemical dataset of 295 granitoid samples from the karelian and kola cratons of the fennoscandian shield we divide neoarchean juvenile extracted from oceanic crust or mantle granitoids into three groups 1 low hree heavy rare earth elements ttgs tonalite trondhjemite granodiorite high sio2 low mg low hree higher sr lower ybn and higher nb ta 2 high hree ttgs slightly lower range of sio2 larger range of mgo contents and higher cr and ni contents high hree lower sr higher ybn and lower nb ta and 3 high ba sr sanukitoids medium hree high mg and high k ba sr the main difference between the low and high hree groups lies in their pressure sensitive element contents which indicates high pressure melting conditions for the low hree group and low pressure conditions for the high hree group a possible tectonic scenario for the genesis of the two groups is an incipient hot subduction underneath a thick oceanic plateau protocrust melting in the lower part of thick basaltic oceanic crust could produce ttgs of the low hree type whereas low pressure melting of subducting slab and possible interactions with the mantle wedge at shallow depths would be capable of generating high hree ttgs the third group of archean high ba sr sanukitoids was formed after the ttgs their low sio2 and high mg k ba sr contents suggest an origin by melting in an enriched metasomatized mantle source probably as a result of a slab breakoff following a continental collision or attempted subduction of a thick oceanic plateau ttg protocontinent such hypothesis is supported by numerical modeling results that suggest an increased occurrence of slab breakoff in the archean which locally increased temperatures within the mantle wedge more frequent breakoff resulted because subducting plates were weaker due to rheologically thinner lithosphere and a thicker basaltic crust and tensile stresses within the subducting plate were larger due to a thick crust that transforms from buoyant basalt to dense eclogite

strain accumulation in southern california 1973 1984 repeated surveys of selected lines from five trilateration networks along the san andreas fault in southern california have been used to deduce the 1973 1984 strain accumulation records at five localities the secular rate of engineering shear strain accumulation is about 0 3 rad yr with the plane of maximum shear parallel to the local strike of the san andreas fault the secular rate of accumulation of areal dilatation is negligible the data were examined to detect evidence for fluctuations in the rate of strain accumulation for this examination 19 lines were removed from the data set four because they exhibited an obvious coseismic offset and 15 others because they contained at least one very anomalous measurement that could reasonably be attributed to a survey blunder the incidence of such blunders appears to be one in every 75 measurements the remaining data consist of 104 lines with an average of 10 measurements each although the strain accumulation plots for the five networks may exhibit marginally significant temporal fluctuations we are not convinced that those fluctuations are greater than could be attributed to survey error in particular we are unable to demonstrate that the 1973 1979 southern california strain anomaly reported by savage and others is real given the uncertainty in the random and systematic errors in measurement the strain measurements in southern california are marginally consistent with linear in time strain accumulation the strain accumulation plots for the salton network clearly established that unlike the deformation reported after the 1940 imperial valley earthquake no acceleration in the shear strain rate has yet been observed following the 1979 imperial valley earthquake

strain accumulation in southern california 1973 1980 frequent surveys of seven trilateration networks in southern california over the interval 1973 1980 suggest that a regional increment in strain may have occurred in 1978 1979 prior to 1978 and after late 1979 the strain accumulation has been predominantly a uniaxial north south compression this secular trend was interrupted sometime in 1978 1979 by an increment in both north south and east west extension in five of the seven networks the onset of this change appears to have occurred first in the networks farthest south the changes occurred without any unusual seismicity within the networks but the overall seismicity in southern california was unusually low prior to and has been unusually high since the occurrence the average principal strain rates for the seven networks in the 1973 1980 interval are 0 17 mu strain yr north south contraction and 0 08 mu strain yr east west extension although the observed increment in strain could be related to unidentifed systematic error in the measuring system a careful review of the measurements and comparison with three other measuring systems reveal no appreciable cumulative systematic error

formation of archean 3600 2500 ma continental crust in the dharwar craton southern india abstract the generation preservation and destruction of continental crust on earth is of wide interest in understanding the formation of continents cratons and supercontinents as well as related mineral deposits in this contribution we integrate the available field petrographic geochronologic elemental nd hf pb isotope data for greenstones ttg gneisses sanukitoids and anatectic granites from the dharwar craton southern india this review allows us to evaluate the accretionary processes of juvenile crust mechanisms of continental growth and secular evolution of geodynamic processes through the 3600 2500 ma window hence providing important insights into building of continents in the early earth the dharwar craton formed by assembly of micro blocks with independent thermal records and accretionary histories the craton can be divided into three crustal blocks western central and eastern separated by major shear zones the western block contains some of the oldest basement rocks with two generations of volcano sedimentary greenstone sequences and discrete potassic plutons whereas the central block consist of older migmatitic ttgs abundant younger transitional ttgs remnants of ancient high grade supracrustal rocks linear volcanic dominated greenstone belts voluminous calc alkaline granitoids of sanukitoid affinity and anatectic granites in contrast the eastern block comprises younger transitional ttgs abundant diatexites thin volcanic sedimentary greenstone belts and calc alkaline plutons published geochronologic data show five major periods of felsic crust formation at ca 3450 3300 ma 3230 3150 ma 3000 2960 ma 2700 2600 ma and 2560 2520 ma which are sub contemporaneous with the episodes of greenstone volcanism u pb ages of inherited zircons in ttgs as well as detrital zircons together with nd pb hf isotope data reveal continental records of 3800 3600 ma the u pb zircon data suggest at least four major reworking events during ca 3200 ma 3000 ma 2620 2600 ma and 2530 2500 ma corresponding to lower crustal melting and spatially linked high grade metamorphic events the ttgs are sub divided into the older 3450 3000 ma ttgs and the younger 2700 2600 ma transitional ttgs the older ttgs can be further sub divided into low al and high al groups elemental and isotopic data suggest that the low al type formed by melting of oceanic island arc crust within plagioclase stability field in contrast the elemental and isotopic features for the high al group suggest derivation of their magmatic precursor by melting of oceanic arc crust at deeper levels 55 65 km with variable garnet and ilmenite in residue the transitional ttgs likely formed by melting of composite sources involving both enriched oceanic arc crust and sub arc mantle with minor contamination of ancient crustal components the geochemical and isotopic compositions of granitoids with sanukitoid affinity suggest derivation from enriched mantle reservoirs finally anatectic granites were produced by reworking of crustal sources with different histories in the light of the data reviewed in this contribution we propose the following scenario for the tectonic evolution of the dharwar craton during 3450 3000 ma ttgs sources oceanic arc crust formed by melting of down going slabs and subsequent melting of such newly formed crust at different depths resulted in ttg magmas on the contrary by 2700 ma the depth of slab melting increased melting of slab at greater depth alongside the detritus results in enriched melts partly modified the overlying mantle wedge subsequent melting of such newly formed enriched oceanic arc crust and surrounding arc mantle generated the magmatic precursor to transitional ttgs finally at ca 2600 2560 ma eventual breakoff of down going slab caused mantle upwelling which induced low degree 10 15 melting of overlying enriched mantle at different depths thereby generating the sanukitoid magmas which upon emplacement into the crust caused high temperature metamorphism reworking and final cratonization the crustal accretion patterns in the dharwar craton share similarities with those in other archean cratons such as the bundelkhand craton in central india pilbara yilgarn craton in western australia southern africa swaziland and limpopo belt north china craton tanzania craton antongil craton ne madagascar

the affinity of archean crust on the yilgarn albany fraser orogen boundary implications for gold mineralisation in the tropicana zone abstract craton margins can be subject to a wide array of gold genesis and redistribution processes although high grade terrains on craton margins are frequently viewed as less prospective than lower grade counterparts in contrast to this the high grade tropicana zone a newly defined archean crustal component on the eastern margin of the yilgarn craton within the albany fraser orogen afo contains a significant proterozoic gold deposit this deposit and zone comprise mid amphibolite to granulite facies gneissic rocks with evidence of partial melting and granite injection the tropicana zone contains significant low si lile enriched granites classed as sanukitoids along with the distinctive compositions the rarity of these rocks within any archean craton suggests that the granitoid protoliths represent a single suite emplaced during one event due to the intense granulite facies overprinting of the tropicana zone rocks determination of the magmatic protolith age for these sanukitoids is challenging nonetheless the best age estimate for magmatism is 2692 16 ma based on the youngest zircons preserving textural evidence of growth within a viscous silicate melt this age is older than compositionally similar magmatism found within the yilgarn craton although a sanukitoid in the northern foreland of the afo has a similar age furthermore the granulite facies metamorphic zircon growth in the tropicana zone at 2718 2554 ma was prolonged compared to that in the yilgarn craton nonetheless the hf isotopic signature of the tropicana zone zircon shares strong similarity to that from the eastern goldfields superterrane of the yilgarn craton this implies that the tropicana zone reflects a deeper crustal level of the yilgarn craton exhumed and thrust nw an unknown distance over the craton edge in addition we observe that the granulite facies zircons have a less radiogenic hf isotope signature than the preserved pre metamorphic zircon cores based on correlations with alpha dose u and th content and 176hf 177hf we suggest this reflects the preferential destruction and release of unradiogenic hf from inherited zircon whereas the protolith sanukitoid zircon with lower u and th content was more resistant to mobilisation during high grade metamorphism we note this situation may be a more general response of the hf isotopic system in which zircon grown in a more mafic melt is less likely to contribute to the metamorphic hf reservoir than its felsic counterpart juvenile granitic veins dated at c 1780 ma intruded into the tropicana zone indicate that the tropicana zone was structurally emplaced at or before c 1780 ma given similar proterozoic magmatic events are well documented from para autochthonous adjacent units re os dating of pyrite coeval with one generation of gold in these rocks indicates model ages of c 2100 ma supportive of a palaeoproterozoic age of mineralisation this mineralisation event is distinct from major proterozoic tectonothermal events elsewhere in the afo sanukitoid magmas are well known for gold fertility and were likely the original source of gold in the tropicana zone which was subsequently concentrated into brittle structures during several episodes gold mineralisation post dated peak metamorphic conditions and is significantly younger than gold mineralisation within other parts of the adjoining yilgarn craton

neoarchean crustal recycling and mantle metasomatism hf nd pb o isotope evidence from sanukitoids of the fennoscandian shield abstract the growing knowledge of the geological record reveals evidence of crustal recycling in the archean eon in order to assess the role of recycling of crust into the mantle we have analyzed radiogenic hf in zircon as well as whole rock nd and pb isotope compositions of mantle derived granitoids of the sanukitoid series in the neoarchean karelian province fennoscandian shield homogeneous initial hf and nd values suggest that sanukitoids are derived from well mixed source s limited scatter in the initial pb isotope data within intrusions as well as in other radiogenic isotopes point to effective mixing processes in the mantle o isotope data for zircon from karelian sanukitoids indicate a dominant mantle source 18 o 5 5 6 1 with minor contributions from sources with elevated 18 o 7 0 to 8 5 such as sediments and altered upper oceanic crust our results suggest that the parental melts of sanukitoids are mixtures of depleted mantle and recycled crustal components a slab breakoff at the end stage of subduction is a plausible trigger mechanism for sanukitoid magmatism and it explains variable contributions from different 18 o sources

the archaean sanukitoid series of the baltic shield geological setting geochemical characteristics and implications for their origin abstract archaean high mg granitoids sanukitoids occur in the karelian granite greenstone terrain in the baltic shield in two distinct zones in the west of the shield sanukitoid intrusions formed between 2700 and 2720 ma and consist of a single igneous phase that varies in composition from diorite to granite in the eastern part of the shield sanukitoid intrusions formed between 2730 and 2745 ma and are strongly differentiated varying in composition from ultramafic to felsic all the sanukitoids are enriched in light rare earth elements lree la 80 ppm ce 150 ppm la n yb n 30 40 sr 2000 ppm ba 2500 ppm p 2 o 5 1 5 alkalis na 2 o k 2 o 5 10 possess high mg values 0 50 0 65 and show a negative nb ta anomaly they are spatially and temporally related to syenite intrusions and lamprophyre dykes sanukitoid intrusions in the western and eastern zones differ in composition in the west they have higher sio 2 mainly 60 and lower alkalis sr ba lree than in the eastern zone intrusions the most differentiated intrusion the panozero intrusion in the eastern zone was formed in two magmatic cycles separated by ductile deformation in the first cycle ultramafic to monzonitic rocks formed whereas in the second cycle the magmas were monzodioritic to quartz monzonite ultramafic and mafic rocks make up about 10 of the outcrop and occur as enclaves in monzonites and monzodiorites and as dykes implies a number of discrete magmatic events all rocks of the panozero intrusion have high k 2 o and the composition of the initial melt calculated from the weighted average of the first cycle magmas is monzodiorite sio 2 52 mg 0 55 na 2 o k 2 o 6 the presence of magmatic hornblende and biotite a high carbonate content widely distributed explosive breccias and evidence of liquid immiscibility are consistent with a high h 2 o co 2 content in the sanukitoid melt the geodynamic model which most satisfactorily explains our geological and geochemical observations is the formation of the karelian sanukitoids in a cratonic environment adjacent to the belomorian karelian suture

forecast model for large and great earthquakes in southern california an earthquake instability model is used to compute theoretical fault slip and ground surface deformation before possible future earthquakes on the san andreas fault in southern california the quasistatic model represents the earth s crust by an elastic half space and the san andreas imperial cerro prieto and san jacinto faults by flat rectangular surfaces whose strikes approximate the actual local strikes the seismogenic zone of the san andreas fault is represented by a brittle strain softening patch extending from the ground surface to 11 km depth and from parkfield to the salton sea 500 km the strength of the patch varies along strike and unstable failures of parts of the patch are earthquake analogs failed areas heal immediately after instability for the model to reproduce the lengths slips and times of earthquakes since 1080 a d reported by k sieh and others the patch must be divided into five sections along strike the sections have alternately low and high strength with the two strongest sections being roughly coincident with the major bends of the san andreas fault ten to twenty years before unstable slippage of patch areas portions of the patch bottom begin to fail stably aseismically the stable failure causes accelerating fault slip at depth and at the fault trace as well as anomalous changes in lengthening rates of trilateration lines in the model simulation the next two sections to fail unstably in the future are just north of the salton sea and just south of parkfield rupture lengths are about 100 km and 40 km at favorable locations precursory anomalies of fault slip and trilateration line length become large enough to be detected in field data a few years before each earthquake

subduction related shoshonitic and ultrapotassic magmatism a study of siluro ordovician syenites from the scottish caledonides syenites are important or predominant components of several plutonic complexes emplaced between 456 and 415 ma along the nw margin of the caledonian orogenic belt adjacent to the lewisian foreland in w and nw scotland although there are in detail chemical differences between the syenites from each centre they form a well defined compositional group overall ratios amongst their trace elements especially very high values of la nb are quite different from those trachytes and syenites formed by fractional crystallisation of ocean island basalts and their continental equivalents emplaced in regions of anorogenic crustal tension instead the scottish caledonian syenites closely resemble chemically the fractional crystallisation residua of potassic subduction related magmas such as the shoshonitic series a comendite minor intrusion from a swarm associated with the loch borralan and loch ailsh syenitic complexes is remarkably similar in composition to recent obsidian from the shoshonitic volcano of lipari in the aeolian arc published sr and pb isotopic ratios preclude a significant component of either upper proterozoic moine schists or lower crust granulite facies archaean lewisian or proterozoic grenvillian gneisses in all these syenites except in local syenitic facies of the glenelg ratagain complex fractional crystallisation appears to be the mechanism by which the liquids which formed these syenites evolved from basic parental magmas the phases involved in this process may have included plagioclase alkali feldspar pyroxene amphibole biotite garnet fe ti oxide sphene allanite apatite zircon and zirconolite and therefore all the ratios amongst even the so called incompatible elements may have changed during the evolution of the leucocratic magmas nevertheless a detailed study of the glen dessarry complex shows that the changes are insufficient to disguise the geochemical nature of the parental magmas these appear to be picritic shoshonite mgo 15 ni 400ppm la yb 20 la nb 5 for the glen dessarry loch borralan and loch ailsh syenites and picritic ultrapotassic magmas mgo 15 ni 400 ppm la yb 60 la nb 7 such as would crystallise to minettes for the loch loyal and glenelg ratagain syenites mafic shoshonites were erupted amongst the 410 ma lome lavas of this region and also occur as widespread approximately contemporaneous volcanic feeder plugs minettes of similar age are also common as dykes in nw scotland numerous large tonalite granite complexes with minor diorites and gabbros were emplaced in w and nw scotland between 435 and 400 ma these are generally acknowledged to be mixtures of magmas from crustal and mantle sources their more mafic members show compositional features such as very high ba and sr which group them with the rare syenites and the lorne lavas of the same region into a distinctive geochemical province within which shoshonitic and allied magmas were the mantle derived component two models are presented to account for the generation of strongly potassic subduction related magmas several hundred km behind a nw directed subduction zone or during the period immediately following continental collision

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

interseismic coupling and refined earthquake potential on the hayward calaveras fault zone interseismic strain accumulation and fault creep is usually estimated from gps and alignment arrays data which provide precise but spatially sparse measurements here we use interferometric synthetic aperture radar to resolve the interseismic deformation associated with the hayward and calaveras faults hf and cf in the east san francisco bay area the large 1992 2011 sar data set permits evaluation of short and long wavelength deformation larger than 2 mm yr without alignment of the velocity field to a gps based model our time series approach in which the interferogram selection is based on the spatial coherence enables deformation mapping in vegetated areas and leads to refined estimates of along fault surface creep rates creep rates vary from 0 2 mm yr on the northern cf to 14 2 mm yr on the central cf south of the hf surface junction we estimate the long term slip rates by inverting the long wavelength deformation and the distribution of shallow slip due to creep by inverting the remaining velocity field this distribution of slip reveals the locations of locked and slowly creeping patches with potential for a m6 8 0 3 on the hf near san leandro a m6 6 0 2 on the northern cf near dublin a m6 5 0 1 on the hf south of fremont and a m6 2 0 2 on the central cf near morgan hill with cascading multisegment ruptures the hf rupturing from berkeley to the cf junction could produce a m6 9 0 1 the northern cf a m6 6 0 1 the central cf a m6 9 0 2 from the junction to gilroy and a joint rupture of the hf and central cf could produce a m7 1 0 1

neoarchean magmatic arc in the western liaoning province northern north china craton geochemical and isotopic constraints from sanukitoids and associated granitoids abstract the neoarchean western liaoning basement terranes in the northern part of north china craton chiefly consist of tholeiitic basalts in the north ttg gneisses and metavolcanic rocks in the northwest and k rich granitoids in the southeast in the southeastern zone porphyritic monzodioritic quartz monzodioritic granodioritic monzogranitic mqgm gneisses are the major lithological assemblage and locally contain minor xenoliths of ttg gneisses based on the major mafic mineral phases the porphyritic mqgm gneisses can be divided into amphibole dominated and biotite dominated groups zircon u pb isotopic dating indicates that the amphibole dominated mqgm gneisses biotite dominated mqgm gneisses and tonalitic gneiss xenolith were emplaced during 2546 2529 ma 2546 2531 ma and at 2563 ma respectively the 2563 ma tonalitic gneiss xenolith displays geochemical affinities to high sio 2 adakites and may be formed by the partial melting of descending oceanic slabs with the melt contaminated by mantle peridotite the amphibole dominated mqgm gneisses are geochemically analogous to sanukitoids and their magmatic precursors were formed by partial melting of lithospheric mantle which was metasomatized by dehydration fluids and melts derived from subducted oceanic sediments and slabs the magmatic precursors of the biotite dominated mqgm gneisses were generated by the partial melting of medium k to high k mafic rocks at medium pressures integrated with previous studies on supracrustal sequences and granitoids in western liaoning province the neoarchean lithological assemblages in the southeastern zone were most likely formed in an active continental margin setting

the diversification of granitoids and plate tectonic implications at the archaean proterozoic boundary in the bundelkhand craton central india

slab breakoff a model for caledonian late granite syn collisional magmatism in the orthotectonic metamorphic zone of scotland and donegal ireland abstract none of the existing models for calc alkaline late granite siluro devonian genesis in the metamorphic caledonian orogenic belt of ireland and scotland fully explains their spatial age or chemical character a consistent model must involve the closure of iapetus ocean where slab breakoff is a natural consequence of attempted subduction of continental crust expected outcome is a long linear belt of high k calc alkaline magmas some with characteristic trace element signatures specifically high ba sr and zr other features include the critical magmatic association of coeval appinite and granite rapid uplift erosion and the low grade regional metamorphism in the southern uplands the linear heat pulse on breakoff is spatially intensity and time limited producing small volume melts emplaced as separated plutons over a short time span magmatism in the caledonian metamorphic belt is accurately accounted for by slab breakoff on collision of baltica with the scoto greenland margin during the scandian orogeny following iapetus ocean closure the two chemically isotopically and areally distinctive suites in the metamorphic belt in scotland viz the argyll and cairngorm suites can be modelled by reference to the donegal granites where sequential partial melting of new lamprophyric underplated crust then shallower old crust as heat conduction moved up through the crust on slab breakoff produced magmas characteristic of the two suites

a neoarchean k rich granitoid belt in the northern north china craton abstract the archean metamorphic basement in the southeastern part of eastern hebei to western liaoning provinces northern north china craton is dominated by neoarchean k rich granitoids with a small amount of neoarchean supracrustal rocks and na rich dioritic tonalitic trondhjemitic granodioritic gneisses and minor paleo to mesoarchean rocks the paleo to mesoarchean lithological signatures include ttg gneisses and supracrustal rocks at the caozhuang and caochang areas the neoarchean k rich granitoids form a ca 350 km long belt extending in a ne direction and primarily consist of porphyritic monzodioritic quartz monzodioritic granodioritic monzogranitic mqgm gneisses and secondary monzogranite syenogranites and charnockites with minor neoarchean ttg gneiss enclaves based on their major mafic mineral phases the mqgm gneisses can be divided into an amphibole dominated group and a biotite dominated group zircon u pb isotopic dating reveals that the caozhuang trondhjemitic gneisses amphibole dominated mqgm gneisses and biotite dominated mqgm gneisses were emplaced at 2 90 ga 2 55 2 53 ga and 2 55 2 53 ga respectively the amphibole dominated porphyritic mqgm gneisses are geochemically analogous to sanukitoids and the sanukitoid magma was derived from the partial melting of lithospheric mantle metasomatized by dehydration fluids and melts from subducted slabs and related sediments following the fractionation of amphibole and clinopyroxene during their magmatic evolution the magmatic precursors of the biotite dominated mqgm gneisses were most likely generated by the partial melting of medium to high k mafic intermediate rocks and locally generated by the partial melting of metagreywackes at medium pressures within the k rich granitoid belt the 2 55 2 53 ga porphyritic mqgm gneisses experienced 2 53 2 51 ga e w extension and strike slip shearing deformation in the jinzhou xingcheng structural domain and diapiric upwelling by the formation of dome structures in the jielingkou anziling suizhong structural domain all these structures then suffered a top to the se nee thrusting in the northern margin during 2 51 2 50 ga the 2 53 2 51 ga dioritic tonalitic trondhjemitic granodioritic gneisses and charnockites in the taipingzhai santunying zunhua structural domain firstly underwent diapiric upwelling during 2 51 2 50 ga then together with the 2 52 2 50 ga volcanic sedimentary rocks in the shuangshanzi qian an lulong structural domain overprinted by nearly n s striking dextral strike slip shearing deformation during 2 50 1 80 ga the temporal spatial relationships petrogenesis and structural patterns of these various neoarchean lithological assemblages confirm that the neoarchean k rich granitoid belt in the northern north china craton was most likely developed in an active continental margin setting and our studies suggest this involved progressively southeastward multi stage retreating oceanic slab subduction and collisions between an oceanic arc and an ancient continental nucleus

sawtooth segmentation and deformation processes on the southern san andreas fault california five contiguous 12 13 km fault segments form a sawtooth geometry on the south ernmost san andreas fault the kinematic and morphologic properties of each segment depend on fault strike despite differences of strike between segments of as little as 3 degrees oblique slip transpression of fault segments within the indio hills mecca hills and durmid hill results from an inferred 8 1 ratio of dex tral slip to convergence across the fault zone triggered slip and creep are confined almost en tirely to transpressive segments of the fault durmid hill has been formed in the last 28 n 6 ka by uplift at an average rate of 3 1 mm a

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

forecasting southern california earthquakes since 1978 and 1979 california has had a significantly higher frequency of moderate to large earthquakes than in the preceding 25 years in the past such periods have also been associated with major destructive earthquakes of magnitude 7 or greater and the annual probability of occurrence of such an event is now 13 percent in california the increase in seismicity is associated with a marked deviation in the pattern of strain accumulation a correlation that is physically plausible although great earthquakes magnitude greater than 7 5 are too infrequent to have clear associations with any pattern of seismicity that is now observed the san andreas fault in southern california has accumulated sufficient potential displacement since the last rupture in 1857 to generate a great earthquake along part or all of its length

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

discrimination and origin of the sanukitoid series geochemical constraints from the neoarchean western karelian province finland abstract neoarchean late to post tectonic sanukitoid intrusions are found in the western part of the karelian province in finland variable sized even grained to k feldspar porphyritic intrusions form a series of diorites tonalites and granodiorites that are calc alkaline to alkali calcic magnesian and mostly peraluminous the major and trace element geochemistry of the intrusions show typical sanukitoid affinities a mantle signature high content of mg ni cr and high mg and enrichment in lile especially k ba and sr the intrusions form a distinctive series that can be distinguished from the ttg series of the karelian province by their high ba sr signature low na 2 o k 2 o ratio and uniform hree pattern the sanukitoid series can be compositionally constrained as follows sio 2 55 70 wt na 2 o k 2 o 0 5 3 mgo 1 5 9 wt mg 45 65 k 2 o 1 5 5 0 wt ba sr 1400 ppm and gd er n 2 6 the probable source was enriched subcontinental lithosphere mantle with high lile concentrations in phlogopite and or sanidine the accumulation of k ba and sr in the mantle source may have occurred as a consequence of two separate metasomatic events 1 by subduction related fluids melts and 2 by metasomatism related to asthenospheric mantle upwelling caused by slab breakoff the slab breakoff at the end stage of subduction is also a viable trigger for the sanukitoid magmatism

neoarchean metagabbro and charnockite in the yinshan block western north china craton petrogenesis and tectonic implications abstract properly calibrating the magmatic record of mantle and crustal origin in archean granite greenstone terranes is crucial for understanding the petrogenetic and geodynamic processes that generated early continental landmasses this geochronological and geochemical study documents a neoarchean bimodal metaplutonic suite of metagabbro and charnockite from the yinshan block north china craton the meta gabbroic rocks show an sio 2 range from 45 9 to 51 7 and high mgo content from 6 7 to 16 4 with enrichment in ba and light rare earth elements la n yb n 3 11 5 99 and depletion in high field strength elements together with their enriched whole rock nd nd t 0 23 to 1 49 and zircon hf hf t 0 1 6 9 isotopic signatures relative to the archean depleted mantle in the craton these rocks are supposed to originate from the second stage high temperature partial melting of refractory depleted mantle that experienced prior basaltic magma extraction and subsequent metasomatism by subduction related fluids the associated charnockites range in sio 2 from 61 3 to 69 6 and exhibit a magnesian calc alkalic and metaluminous character with variable sr y and la n yb n ratios these elemental features plus their evolved isotopic compositions nd t 0 93 1 85 zircon hf t 0 3 to 2 5 are consistent with partial melting of newly underplated mafic lower crustal protolith in combination with widespread occurrence of metasomatized lithospheric mantle derived magmas e g high mg basalts sanukitoid suites and juvenile crust extracted potassic granites in the ncc during late neoarchean time such a mafic and felsic magma association not only attests to the establishment of a craton scale subduction related metasomatized sub continental lithospheric mantle but also encapsulates a scenario of coupled lithospheric mantle crust formation at 2 7 ga and juvenile crustal reworking at 2 5 ga within a modern style convergent continental margin possibly featuring episodic slab break off events

late archean high mg granitoids sanukitoids in the southern karelian domain eastern finland pb and nd isotopic constraints on crust mantle interactions late archean ca 2 73 ga porphyritic high k and high mg granitoids in the nilsia and lieksa areas eastern finland have geochemical signatures similar to those of high mg sanukitoid series from other parts of the karelian domain of the fennoscandian baltic shield and the archean sanukitoid suites from canada the nilsia and lieksa granitoids have low sio2 contents 62 7 67 0 and high mg numbers 0 45 0 52 they are enriched in k2o 2 40 4 73 wt p2o5 0 25 0 42 wt sr 610 850 ppm ba 1200 2300 ppm cr 40 80 ppm and lree la yb n 19 65 they are characterized by a negative eu anomaly eu eu 0 53 0 81 and show strong depletion in u high th u ratio low u pb ratio high 2 values for the source 9 positive nd 2 7 ga values of 0 3 1 4 and nd depleted mantle model ages 2 75 2 86 ga the high 2 values pointing to a significantly older crustal source apparently contradicts the positive nd 2 7 ga values supporting a mantle origin the geochemical and isotopic data suggest that the nilsia and lieksa granitoids originated at ca 2 73 ga from a mantle wedge source enriched in lile u th and pb by recycling of continental material in subduction related slab dehydration processes shortly up to 200 ma before melting a considerably large amount of crustal lead was contributed from subducting sediments into the overlying mantle wedge consequently the isotopic composition of mantle wedge lead was overprinted by crustal lead isotope signatures it is suggested that crustal recycling through subduction zone processes played an important role for the enrichment of the mantle wedge and generation of mantle derived high granitoids in the archean

high magnesian granitoids in the precambrian continental crust implication for the continuum between ferro potassic and magnesio potassic rock suites abstract ferro potassic fe k to magnesio potassic mg k hornblende biotite granitoids hbgs with a wide range of sio2 from 52 to 77 wt are typical of precambrian continental crust and are generally related to late and post collisional orogenic events despite their broadly uniform mineralogy and tectonic environment the chemical compositions of these granites suggest different sources from lower crust for the fe k suites to enriched mantle for the mg k counterparts here we propose a classification of the magnesian rocks into moderate mg high mg and ultra mg with corresponding examples from various parts of the world such as the closepet type sanukitoids and their high mg counterparts of the elan type the elan type granitoids are characterized by the highest mgo cr ni end t and lowest tio2 feot feot mgo contents among all the precambrian hbgs and are hence close to a true end member the precambrian hbgs show common features such as a wide range of sio2 contents enrichment in lile k ba sr lree nb ti negative primitive mantle normalized anomalies and weak negative or no eu anomalies in intermediate suites the mg of magmatic and cumulus relict amphiboles displays a compositional array of ultra mg to fe granites and shows positive correlation with the whole rock mg continuum between the compositions of mg k and fe k granitoids is reflected in a gradual decrease in mg cr ni of the rocks and mg of the mafic silicates increase in ti p zr y zn u total ree and decrease of the nd initial isotopic composition together with a change in the paragenesis of fe ti oxides we interpret these features to result from mixing of metasomatized mantle and crustal magmas and their homogenization at the lower crust level the lower crustal source component increases from the mg k to fe k series during their passage to higher crustal levels the magmas underwent fractional crystallization and crustal contamination leading to the wide range in silica content

strain rate profile across the elsinore san jacinto and san andreas faults near palm springs california 1973 81 a profile of the strain accumulation rate along a line trending n50 e across the subparallel elsinore san jacinto and san andreas faults near palm springs california has been constructed from trilateration surveys in the 1973 81 interval the strain accumulation is principally right lateral shear across a vertical plane parallel to fault strike n40 w the strain rate profile for that component exhibits two clearly resolved maxima one centered on the san jacinto fault max 0 35 0 02 rad a and the other on the san andreas fault max 0 40 0 02 rad a no maximum is associated with the elsinore fault this result clearly implies that slip at depth on both the san andreas and san jacinto faults is loading the shallower sections of these faults and that eventually rupture can be expected on both

high resolution interseismic velocity data along the san andreas fault from gps and insar 1 we compared four interseismic velocity models of the san andreas fault based on gps observations the standard deviations of the predicted secular velocity from the four models are larger north of the san francisco bay area near the creeping segment in central california and along the san jacinto fault and the east california shear zone in southern california a coherence spectrum analysis of the secular velocity fields indicates relatively high correlation among the four models at longer wavelengths 15 40 km with lower correlation at shorter wavelengths to improve the short wavelength accuracy of the interseismic velocity model we integrated interferometric synthetic aperture radar insar observations initially from advanced land observing satellite alos ascending data spanning from the middle of 2006 to the end of 2010 totaling more than 1100 interferograms with gps observations using a sum remove filter restore approach the final insar line of sight data match the point gps observations with a mean absolute deviation of 1 5 mm yr we systematically evaluated the fault creep rates along major faults of the san andreas fault and compared them with creepmeters and alignment array data compiled in uniform california earthquake rupture forecast version 2 ucerf2 moreover this insar line of sight dataset can constrain rapid velocity gradients near the faults which are critical for understanding the along strike variations in stress accumulation rate and associated earthquake hazard

mantle derived archaean monozodiorites and trachyandesites the 2 680 2 750 myr old1 5 intrusive granite greenstone terranes6 8 in the rainy lake region ontario and in and adjacent to the vermilion district minnesota of the superior province in north america include a wide variety of volcanic and intrusive rocks with initial pb sr and nd isotope ratios close to those for the mantle4 5 9 12 the isotopic constraints require the production of large volumes of silica oversaturated magmas from silica undersaturated mantle within 100 200 myr we present here geochemical data on monzodiorites and trachyandesites from the rainy lake area which are strongly enriched in large ion lithophile elements lile we conclude that they are derived by direct melting of the mantle at depths of 50km in either anhydrous or hydrous conditions their rare earth element ree abundances and initial 143nd 144nd ratios suggest that their mantle sources were enriched in lile shortly before melting the monzodiorites trachyandesites and their granodioritic derivatives may comprise up to 20 of the exposed igneous rocks in the rainy lake region and vermilion district if these rocks are as abundant in other archaean terranes a significant part of the early continental crust could have formed by direct melting of lile enriched mantle

travel time time term and basement depth maps for the imperial valley region california from explosions in this study we have produced maps of reduced travel time for various shot points in the imperial valley a time term map and a basement depth map the time term map effectively integrates all the features seen on individual travel time maps and the basement depth map is derived from the time term map by a simple linear relation the basement depth map represents the depth to the top of metasedimentary basement vp 5 65 km sec in the central imperial valley and the top of crystalline rocks on west mesa and in the chocolate mountains we estimate the standard error in this map to be 0 6 km the basement depth map indicates depths of up to 6 km in the imperial valley and depths generally less than 3 km on west mesa major zones of high gradient in depth separate the imperial valley from west mesa on the west and from the chocolate mountains on the east because west mesa and the chocolate mountains are underlain by different types of basement than is the imperial valley these major zones of high gradient apparently mark the locations of major crustal boundaries most active faults have basement scarps along at least parts of their lengths basement highs with relief as great as 3 km occur under major geothermal areas in the imperial valley presumably indicating the presence of igneous intrusions and or metamorphism of sedimentary rocks to a relatively higher level in the crust

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 geomorphology of the san andreas fault zone in the southern indio hills coachella valley california geomorphic investigation of the san andreas fault zone in the indio hills indicates many tectonically produced landforms including beheaded streams right lateral deflected and offset streams sags shutter ridges pressure ridges and fault scarps near biskra palms an alluvial fan pediment complex has an apparent cumulative offset of about 0 7 km along the mission creek fault zone north branch san andreas fault many of the tectonic landforms as well as the fracture pattern that has developed during the pleistocene are explainable by simple shear or uplift associated with a small left bend in the main trace of the mission creek fault the ratio of vertical to horizontal displacement in the vicinity of the bend is about 0 04 exposed in pushawalla canyon 5 km northwest of the alluvial fan pediment complex are 1 a sequence of stream terraces 2 folded plio pleistocene fanglomerates and 3 an example of stream capture following a right lateral deflection or offset of several hundred metres a left step of the mission creek fault in pushawalla canyon is a probably cause of folds and sporadic uplift that produced the stream terraces possible cause of recent stream capture are 1 juxtaposition of pushawalla canyon with a relict canyon moving northwestward along the mission creek fault or 2 right lateral deflection or offset of pushawalla canyon along the fault with simultaneous headward erosion of a shorter steep stream flowing toward the coachella valley estimation of a slip rate and identification of paleoseismicity for the san andreas fault in the indio hills is difficult however degree of topographic dissection formation and preservation of desert pavement and relative soil profile development suggest that the age of the offset fan may be as old as 70 000 yr but that most likely it is on the order of 20 000 to 30 000 yr these age estimates for the offset fan indicate a minimum slip rate for the san andreas fault of 10 to 35 mm yr with about 23 to 35 mm yr the most likely the pattern of observed offset drainages is complex but suggests that during the past few thousand years creep events or moderately large earthquakes have periodically produced several metres of right lateral displacement

elemental and o sr nd isotope geochemistry of the glen dessarry syenite nw scotland elemental radiogenic isotope sr nd and stable isotope o data from samples of the 456 ma caledonian glen dessarry syenite are all compatible with a two stage crystal fractionation model for the evolution of the magmas locally modified by contamination with a partial melt of the surrounding moine metasediments the early crystallizing phases which controlled melasyenite leucosyenite evolution were biotite calcic clinopyroxene plus minor apatite and titanite whilst in situ crystal liquid separation also involved alkali feldspar and amphibole with minor allanite zirconolite and zircon the diverse accessory mineral suite controlled significant variations in many of the incompatible elements including inordinate zr hf fractionation crustal contamination led to severe disturbance in abundances and inter element ratios of u th zr hf nb ta heavy rees sr and ba the elemental characteristics of the magmas are typical of shoshonitic subduction related suites with high liles relatively low hfses and pronounced negative nb ta anomalies inferred isotopic characteristics of the parent magmas 87 sr 86 sr 0 7040 nd 2 5 and l8 o 7 o are probably derived from a multicomponent source region involving a substantial input from contemporary depleted mantle

oxygen isotope ratios of archean plutonic zircons from granite greenstone belts of the superior province indicator of magmatic source zircons commonly preserve primary magmatic oxygen isotope ratios even through high grade metamorphic events unlike quartz which more readily loses its primary 18o value by subsolidus exchange intrusive bodies from the superior province canada have an average 18o zircon of 5 8 0 6 n 59 rocks those from granite greenstone belts have an average 18o zrc 5 8 0 6 n 55 in contrast to those from metasedimentary belts that average 18o zrc 6 7 0 2 n 4 the 18o zircon values from granite greenstone belts indicate a maximum allowable input of 14 supracrustal high 18o material into archean magmas of the superior province relative to mantle 18o values igneous bodies of the superior province have been separated into two groups based on geochemistry unenriched plutons and sanukitoids magmatic oxygen isotope ratios inferred from these zircons indicate up to a subtle but significant division of 1 between the two geochemical sets of rocks this distinction is apparent only in the 18o zrc and not in more commonly analyzed less refractory minerals such as quartz and feldspar oxygen isotope data correlate with geochemical modeling of sanukitoids the average 18o zrc for sanukitoids is 6 4 0 2 in comparison to 5 5 0 4 for unenriched plutons there is almost no overlap in values the elevation of sanukitoid 18o zrc indicates input from a high 18o source such as fluids from the subducting oceanic crust melts of subducted sediments or continental crust all of the plutons analyzed in this study have been dated by u pb zircon techniques and the combination of u pb ages and 18o zrc indicates little variability of 18o versus age during archean plutonism in the superior province therefore recycling of sediments and other high 18o sources was not a dominant process during crustal growth from 3003 to 2670 ma in the superior province

early paleozoic high mg granodiorite from the erlangping unit north qinling orogen central china partial melting of metasomatic mantle during the initial back arc opening abstract this study discussed the petrological classification petrogenesis and tectonic significance of early paleozoic high mg granodiorite from the erlangping unit in the north qinling orogen to achieve this target we conducted integrated investigation of in situ zircon u pb dating whole rock geochemical as well as sr nd hf o isotopic compositions for the kanfenggou pluton from the erlangping unit la icp ms zircon dating for the kanfenggou samples yields u pb ages of 442 9 6 2 and 438 0 6 7 ma suggesting that the pluton was emplaced at ca 440 ma whole rock geochemical compositions of the samples display intermediate sio 2 60 48 64 67 wt and k 2 o 1 21 to 2 10 wt but high al 2 o 3 15 44 to 16 51 wt and na 2 o 4 01 to 4 81 wt contents the granodiorite samples are characterized by elevated mgo ranging from 2 30 to 3 44 wt and mg values of 53 35to 56 66 implying they are high mg granodiorites they are characterized by very high ba 524 1132 ppm and sr 684 980 ppm contents but depleted in hree and high la yb n ratios of 6 34 to 16 5 and slightly negative to weak positive eu anomalies eu eu 0 68 1 09 these evidence that the kanfenggou pluton belongs to the sanukitoid series the high mg granodiorite samples exhibit a mantle signature with high mg values 53 35 56 66 cr 45 8 to 93 3 ppm and ni 28 2 to 48 2 ppm contents but enriched in lile pointing to an enriched mantle source the samples show relatively depleted radiogenic isotopic compositions with initial 87 sr 86 sr ratios varying from 0 7044 to 0 7047 e nd t values from 0 31 to 4 21 and zircon e hf t values from 7 3 to 8 3 the zircons have a mean 18 o value of 5 20 0 17 based on the trace element geochemical features the metasomatic agent was suggested to be the fluids generated from dehydration of subducted slab therefore we suggest two stage processes for the formation of the erlangping high mg granodiorites 1 interaction between slab fluids and mantle peridotite 2 partial melting of metasomatized mantle peridotite caused by the asthenosphere mantle upwelling and the initial back arc opening resulted from the oceanic slab rollback

the velocity field along the san andreas fault in central and southern california the velocity field within a 100 km broad zone centered on the san andreas fault between the mexican border and san francisco bay has been inferred from repeated surveys of trilateration networks in the 1973 1989 interval the velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the san andreas fault in the transverse ranges of southern california across strike profiles of the fault parallel component of velocity exhibit the expected sigmoidal shape whereas across strike profiles of the fault normal component of velocity are flat and featureless no significant convergence upon the fault is observed even along the big bend sector of the fault simple dislocation models can explain most of the features of the observed velocity field but those explanations are not unique about 35 mm yr of relative plate motion is accounted for within the span of the trilateration networks geologic studies indicate that the secular slip rate on the san andreas fault is about 35 mm yr the agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes the relative motion observed across the san andreas fault 35 mm yr plus that observed across the eastern california shear zone 8 mm yr accounts for most 43 mm yr of the observed north america pacific relative plate motion 47 mm yr

chemical variation modal composition and classification of granitoids pdf file same as figure 11 of main text using sio2 diagram is defined as al na k ca in atomic proportions i e the parameter such that al ca na k thus a cnk 1 corresponds to 2 and a nk 1 to 0 see main text