geological implications of the 0212 earthquake in 2014 at the tatun volcano group of taiwan synergistic effects of volcanic and faulting activities abstract on february 12 2014 an ml 4 2 earthquake named 0212 eq occurred at the tatun volcano group tvg in northern taiwan seismic data from both the regional broadband array in taiwan and a local dense seismic network in the tvg indicate that the 0212 eq was located at a depth of 4 3 km near shamoshan one of the latest eruptive units in the tvg referring to the aftershocks surrounding the 0212 eq we further found that 1 they formed a linear seismic zone dipping 50 towards the southeast to reach the shanchiao fault that cuts through the tvg 2 focal mechanism of more than half of the larger aftershocks md 1 5 matched this linear seismic zone for a normal faulting and 3 the seismic b value was calculated to be 3 55 they are used to delineate the geometry of the shanchiao fault at the upper crust and to infer that localized geothermal fluid might have affected the activity of aftershocks as manifested by the very high seismic b value the strongly compensated linear vector dipole of the centroid moment tensor suggests the 0212 eq had a non double couple source resulted from the gravitational collapse thus we conclude that the 0212 eq was a combined synergistic effect of a collapsed reservoir filled with volcanic fluids and faulting activities along the shanchiao fault

geochemistry geochronology and tectonic setting of early cretaceous volcanic rocks in the northern segment of the tan lu fault region northeast china abstract we present new geochemical and geochronological data for volcanic and related rocks in the regions of the jia yi and dun mi faults in order to constrain the late mesozoic tectonic evolution of the northern segment of the tan lu fault zircon u pb dating shows that rhyolite and intermediate mafic rocks along the southern part of the jia yi fault formed at 124 and 113 ma respectively whereas the volcanic rocks along the northern parts of the jia yi and dun mi faults formed at 100 ma the rhyolite has an a type granitoid affinity with high alkalis low mgo ti and p contents high rare earth element ree contents and ga al ratios enrichments in large ion lithophile liles e g rb th and u and high field strength element hfses e g nb ta zr and y and marked negative eu anomalies these features indicate that the rhyolites were derived from partial melting of crustal material in an extensional environment the basaltic rocks are enriched in light rees and liles e g rb k th and u and depleted in heavy rees hfses e g nb ta ti and p and sr these geochemical characteristics indicate that these rocks are calc alkaline basalts that formed in an intraplate extensional tectonic setting the dacite is a medium to high k calc alkaline i type granite that was derived from a mixed source involving both crustal and mantle components in a magmatic arc therefore the volcanic rocks along the jia yi and dun mi faults were formed in an extensional regime at 124 100 ma early cretaceous and these faults were extensional strike slip faults at this time

geochronology and geochemistry of the triassic bimodal volcanic rocks and coeval a type granites of the olzit area middle mongolia implications for the tectonic evolution of mongol okhotsk ocean abstract the olzit volcanism in middle mongolia comprises a bimodal suite of basalts and peralkaline rhyolites adjacent to the main mongolia lineament the basalts are characterized by enrichment in lile and lree and depletion in hfse with typical sr nd isotopic signatures end t 2 50 to 0 38 and 87sr 86sr i 0 7058 0 7063 indicating they were likely derived from partial melting of an enriched lithospheric mantle modified by subducted slab derived fluids the rhyolites show a close affinity to a type granites with enrichment in lile and lree and depletion in nb ta and ti they also show a significant negative eu anomaly and have end t values ranging from 0 50 to 1 38 and initial 87sr 86sr ratios ranging from 0 7022 to 0 7200 suggesting the rhyolites stem from partial melting of crustal rocks rather than fractional crystallization of the basaltic melt the rhyolite porphyry yields a shrimp zircon u pb age of 207 2 ma mswd 1 42 indicating the bimodal volcanic suite formed in the late triassic the miarolitic per alkaline granite and biotite bearing granite which are associated with the bimodal volcanic rocks show typical a type granitic geochemical affinity with end t 0 89 0 91 and 87sr 86sr i 0 7021 0 7043 indicating they are likely generated by partial melting of crustal rocks similar to the rhyolitic end member of bimodal suite the miarolitic per alkaline granite and biotite bearing granite yielded shrimp zircon u pb ages of 209 2 ma mswd 0 91 and 213 3 ma mswd 1 65 respectively which are nearly coeval with the age of the bimodal volcanic suites in view of the new geochemical and chronological data in this study we suggest the olzit late triassic bimodal volcanic rocks together with the coeval a type granites represent a back arc basin extensional environment which probably related to the roll back of mongol okhotsk oceanic plate during the southward subduction under the central mongolia microcontinent

nature of three episodes of paleoproterozoic magmatism 2180 ma 2115 ma and 1890 ma in the liaoji belt north china with implications for tectonic evolution abstract three episodes of paleoproterozoic magmatism with distinctively different nature in the liaoji belt of the eastern north china craton are discussed here the 2200 2140 ma liaoji a type granites the 2160 2110 ma haicheng mafic sills and the 1890 ma qingchengzi i type granites the mafeng monzogranitic pluton representative of the liaoji a type granites gives a sims u pb zircon age of 2181 6 ma n 20 mswd 4 3 the qingchengzi plagiogranitic pluton representative of the qingchengzi i type granites gives a sims u pb zircon age of 1891 10 ma n 8 mswd 1 8 the mafeng monzogranites are high in fe ti k but low in mg al and ca they have high abundance of total rees ree 213 346 ppm they are relatively depleted in feldspar compatible elements e g eu and sr and hfses e g nb ta p and ti they have high 10000 ga al ratios of 3 19 3 61 and zr nb ce y concentrations of 472 656 ppm which are typical for a type granite the qingchengzi plagiogranites have relatively high al ca na but low fe ti and k contents they have low abundance of total rees ree 17 6 21 6 ppm they are enriched in liles e g ba k and sr but depleted in hfses e g nb ta p ti and y these features combined with extremely high sr y ratios 327 413 are comparable with those of typical modern adakites the liaoji a type granites show a source same to that of the haicheng mafic sills and they originated from the archean subcontinental lithospheric mantle plus with contamination from the archean granites however the qingchengzi i type granites are interpreted to originate from subducted oceanic crust with significant contributions from sediments the liaoji a type granites and the coeval bimodal volcanism in the liaohe group as well as the haicheng mafic sills may represent episodic magmatism which was related to a protracted intra continental rifting caused by lithospheric extension the ca 1890 ma qingchengzi i type granites and coexisting s type granites as well as the coeval regional metamorphism are favored to represent an active continental magmatism linked to paleoproterozoic subduction

origin of a mesozoic granite with a type characteristics from the north china craton highly fractionated from i type magmas we report geochronological geochemical and isotopic data for the mesozoic shangshuiquan granite from the northern margin of the north china craton the granite is highly fractionated with sio2 74 occurrence of annitic biotite high contents of alkalis k2o na2o rb y nb and heavy rare earth elements high feot mgo low contents of cao al2o3 ba and sr and large negative eu anomalies makes it indistinguishable from typical a type granites a mantle derived origin for the rocks of the granite is not favored because their high initial 87sr 86sr 0 706 and low end t 15 are completely different from either those of the lithospheric or asthenospheric mantle in fact their sr nd isotopes fall within the range of sr nd isotopic compositions of the archean granulite terrains and are comparable to those of mesozoic crustal derived i type granitoids in the region therefore the shangshuiquan granite is considered to be dominantly derived from partial melting of the ancient lower crust its parental magmas prove to be similar to i type magmas and to have undergone extensive fractionation during its ascent this is supported by the fact that some of the nearby hannuoba feldspar rich granulite xenoliths can be indeed regarded as the early cumulates in terms of their mineralogy chemistry sr nd isotopes and zircon u pb ages and hf isotopes it is furthermore argued that some of highly fractionated granites worldwide especially those with a type characteristics and lacking close relationship with unfractionated rocks may in fact be fractionated i type granites this suggestion can explain their close temporal and spatial associations as well as similar sr nd isotopes with i type granites our study also sheds new light on the petrogenesis of deep crustal xenoliths

spatial mapping of b value heterogeneity beneath the rwenzori region albertine rift evidence of magmatic intrusions abstract we report studies conducted on populations of local crustal earthquakes depths 35 km that were triggered beneath the rwenzori region of the albertine rift and then modelled according to the gutenberg and richter 1954 law a total of about 10 000 earthquakes whose location precision is 5 km were available for analysis a glance of the entire catalogue indicated that the data were complete for magnitudes 1 7 to estimate the b value distribution in the region we used the maximum likelihood method of aki 1965 the overview b value map revealed anomalously high b values ranging between 1 00 0 06 to 1 25 0 09 between longitudes 30 00 30 50 and latitudes 0 00 1 25 on the cross section however we observed low b values 0 65 0 03 to 0 88 0 05 that we believe could possibly correspond to the presence of asperities we interpreted these low b values in asperities as signatures indicative of elevated stress levels probably due to material homogeneity in the crust the intermediate b values 0 88 0 05 to 1 04 0 05 observed represent regions that are probably experiencing either high thermal gradients due to thermal upwelling above a hot source or an indication of remnant geothermal effects after past volcanic activity in the rwenzori region high b value anomalies of ranges b 1 04 0 05 1 21 0 09 were observed at different localities we related these anomalous volumes to an increase in material heterogeneity due to the thermal cracking in nearby rocks associated with an active magma body emplaced in the crust whose source is probably in the lithospheric mantle beneath the rwenzori region the high b value signatures observed suggested a possible source of the heat flux for the geothermal activity observed in the rwenzori region

petrogenesis of the dengzhazi a type pluton from the taihang yanshan mesozoic orogenic belts north china craton abstract the voluminous mesozoic monzonitic to monzogranitic rocks in the north china craton ncc mostly show high k calc alkaline and i type granitoids features the dengzhazi granitic pluton however shows features typical of a type granites the a type pluton was emplaced in the taihang yanshan orogenic belts of the northern margin of the ncc with zircon u pb ages of around 140 ma the dengzhazi a type granites are characterized by high sio 2 70 2 77 7 wt k 2 o na 2 o zr nb ga zn and y contents as well as high ga al ratios and extremely low cao ba sr in addition they show high zircon saturation temperatures 870 950 c low water and low oxygen fugacity all these features are consistent with the a type affinity of the pluton in situ hf isotopic analyses for the dated zircons show relatively small range of e hf t 13 to 17 they also have homogeneous initial nd isotopic compositions with e nd t ranging from 15 1 to 16 3 the hf and nd isotopic data suggest that the dengzhazi a type granites originated from a homogeneous crustal source probably the archean mafic intermediate granulites taking into account the high temperatures the low h 2 o and f o 2 of the magma system we believe that partial melting of the granulites should have been triggered by underplating of mantle derived magmas at the base of the mafic lower crust in an extensional regime the dengzhazi a type granite is the oldest pluton of the taihang yanshan mesozoic magma belts signifying the commencement of extensive underplating of mafic magmas and thus of lithospheric thinning in the northern ncc

preliminary result of magnetotelluric soundings in the fold thrust belt of taiwan and possible detection of dehydration abstract until the magnetotelluric mt soundings were conducted in the last two years there was no systematic view of the deep electric conductivity in the fold thrust belt of the taiwan orogen being a typical example of arc continental collision presented in this paper are the initial results and preliminary interpretation of the mt survey in taiwan the determinant response of the impedance tensor was calculated for inversion and occam s inversion which could generate smooth models was mainly used for interpreting mt data at each site the existence of a conductive zone with depths of 10 20 km beneath the island of taiwan is undoubtedly the most important feature found in this study the depths are well correlated with the inferred depth of dehydration reactions of suppe 1981 and the top of the aseismic lower crust observed by wang et al 1994 thus the authors believe that the cause of this conductive zone is probably the fluids released from dehydration reactions additionally close to the lishan fault the mt data show strong distortions which may be the result of induction in more complex three dimensional structures further multi dimensional analysis of the data is required in the future for delineating a more realistic image of the subsurface heterogeneous structure

the petrogenesis of a type magmas from the amram massif southern israel the 550 530ma alkaline magmatic suite of the amram massif southern israel was emplaced during the transition from an orogenic to an intra plate tectonic setting in the northeastern arabian nubian shield ans the suite ranges from 45 6t o 788 wt sio2 and consists of rhyolites alkali quartz syenites quartz syenites monzonites and co magmatic mafic to felsic alkaline dikes these rocks define a continuous chemical evolutionary trend and reveal a correlation between decreasing stratigraphic age and increasing silica content the felsic members of the suite display a type characteristics and are genetically linked through fractionation to the more mafic ones moderately positive initial end values a2 05 low initial 87 sr 86 sr values 07036 2 high mgo and fe2o3 concentrations 410 895 and 100 125 wt respectively and relatively flat rare earth element patterns la yb na 64 09 in the amram mafic dikes 456 495 wt sio2 suggest their derivation from the sub continental lithospheric mantle above the garnet stability zone the melts program was used to quantitatively model the chemical evolution of the suite extensive anhydrous fractionation 490 of plagioclase alkali feldspar clinopyroxene olivine and minor timagnetite and apatite from parental mafic magmas represented by the amram mafic dikes produced the rhyolitic compositions as well as the intermediate members of the suite this suggests the presence of a large unexposed body of cumulate rocks at depth as well as fusion of a large source region equivalent to an 5km layer in the lithospheric mantle regarded as a representative example for similar a type outcrops in this region this petrogenetic model further suggests that neoproterozoic early cambrian a type magmatism in the northeastern ans represents a significant post orogenic addition of mantlederived material to the juvenile crust this magmatic episode was of a similar magnitude to that of the cenozoic extensionrelated alkaline volcanism of the arabian plate

earthquake magnitude recent research and current trends abstract the magnitude recommendations adopted by the iaspei assembly at zurich in 1967 have had both a stabilizing and a stimulating effect on magnitude determinations and related research from 1967 onwards one magnitude research paper has appeared on the average almost every week thus making this parameter the most studied one in seismology new facilities and more accurate methods e g concerning instrumental equipment and interpretation techniques have made it possible to improve earlier achievements the application of magnitude scales has been extended in all respects e g with regard to epicentral distances focal depths wave types and wave periods magnitude frequency relations have become the most investigated equations within seismology observationally as well as theoretically they have wide applications e g for estimating the maximum magnitudes of future earthquakes an important item in earthquake prediction the magnitudes provide significant information on other source parameters such as wave energy fault length seismic moment relations between different types of magnitude yield valuable information on source properties for instance relations between magnitudes based on body and surface waves are used for efficient discrimination between earthquakes and underground explosions it is our purpose to review the magnitude development in the post zurich period 1967 1980 partly for geologists tectonophysicists and engineers who need an overview partly for seismologists who need an introduction to an overwhelmingly comprehensive literature

geochemical and sr nd pb isotopic data bearing on the origin of pan africangranitoids in the kid area southeast sinai egypt the kid plutonic suite in southeast sinai egypt is composed of 1 a gabbro diorite complex 2 quartz monzodiorite 3 granodiorite monzogranite association 4 syenogranite major and traceelement analyses and radiogenic isotope data rb sr sm nd and pb pb are presented for these rocks rb sr isochrons indicate ages of 581 11 ma 576 11 ma and 570 4 ma for the quartz monzodiorite granodiorite monzogranite association and syenogranite respectively the gabbro diorite complex is a layered intrusion varying in sio2 from 42 to 59 wt it shows a calc alkaline trend and the trace element characteristics of arc lavas subsequently this magma fractionated to give quartz monzodiorite andsyenogranite magmas the quartz monzodiorite has low initial 87 sr 86 sr ratios 0 703 and high nd values 4 4 0 3 with trace element characteristics of volcanic arc granites the granodiorite monzograniteassociation has higher initial sr ratio 0 7044 lower nd 1 5 2 7 and relatively high 207 pb 204 pb and 208 pb 204 pb significantly different from those of the older rocks isotopic data and ree modelling suggestthat it formed by partial melting of an early pan african amphibolitic lower crust the syenogranite isa typical highly fractionated post orogenic granite with a deep negative eu anomaly hfse and reeenrichment a 87 sr 86 sr initial ratio of 0 7033 nd of 4 5 0 5 and distinct variations in the 206 pb 204 pbratio the isotopic compositions of sr nd and pb indicate that the syenogranite and the quartzmonzodiorite are comagmatic increasing fluorine concentration from the quartz monzodiorite to thesyenogranite suggests that fluid fractionation involving fluorine complexing played an important role inthe genesis of the syenogranite this process led to the enrichment of hfse and hree to extensivefractional crystallization to changes in the u pb ratios and a distinct variation in 206 pb 204 pb

early cretaceous adakitic lavas and a type rhyolites in the songliao basin ne china implications for the mechanism of lithospheric extension abstract there is a broad consensus that the extensive late mesozoic igneous rocks in ne china were generated in an extensional setting however the timing and mechanism of the lithospheric extension remain controversial to address this we carried out an integrated study involving la icp ms zircon u pb dating and geochemical analyses major elements trace elements and hf isotopes for the early cretaceous adakitic lavas and a type rhyolites of the songliao basin the adakitic lavas are andesites and dacites the u pb dating of zircons from the adakitic lavas and a type rhyolites yielded ages between 115 and 102 ma geochemically the adakitic lavas are characterized by high sr contents 515 1610 ppm and low y 0 98 17 58 ppm and heavy rare earth element hree contents and they therefore have high sr y 51 112 ratios they also exhibit high mg values 36 57 and high contents of mgo 0 56 3 53 wt cr 15 7 87 3 ppm and ni 6 7 44 7 ppm that are comparable with those of high mg adakitic rocks the a type rhyolites show an affinity with aluminous a type magmatic rocks and they are metaluminous to peraluminous a cnk 0 98 1 35 enriched in alkalis ga zr nb and y depleted in sr and p and exhibit fractionated ree patterns with negative eu anomalies eu eu 0 05 0 77 all the primary zircons from the adakitic lavas and a type rhyolites have positive ehf t values of 3 6 to 12 1 and juvenile two stage model tdm2 ages of 934 392 ma the adakitic lavas probably resulted from the partial melting of a delaminated region of the lower continental crust with the magmas subsequently interacting with mantle materials upon ascent while the a type rhyolites were probably generated by the partial melting of a dehydrated charnockitic middle lower crust the data suggest that the adakitic lavas and the a type rhyolites formed in an extensional environment related to the rollback of the subducting paleo pacific plate the upwelling of asthenospheric mantle and local delamination of the lithosphere which were induced by rollback of the subducting paleo pacific plate extended from the great xing an range southeastward through the songliao basin to eastern heilongjiang and jilin provinces giving rise to the southeastward migration of lithospheric extension and extension related volcanism after ca 140 ma

seismicity characteristics of a potentially active quaternary volcano the tatun volcano group northern taiwan the tatun volcano group tvg is located at the northern tip of taiwan near the capital taipei and close to two nuclear power plants because of lack of any activity in historical times it has been classified as an extinct volcano even though more recent studies suggestthattvgmighthavebeenactiveduringthelast20ka inmay2003aseismicmonitoringprojectatthetvgareawasinitiated by deploying eight three component seismic stations some of them equipped with both short period and broadband sensors during the 18 months observation period local seismicity mainly consisted of high frequency earthquakes either occurring as isolated events or as a continuous sequence in the form of spasmodic bursts mixed and low frequency events were also present during the same period eventhoughtheyoccurredonlyrarely arrivaltimesfromeventswithclearp s wavephaseswereinvertedinordertoobtaina minimum 1dvelocity modelwithstation corrections probabilistic nonlinear earthquakelocationswere calculated for allthese events using the newly derived velocity model most high frequency seismicity appeared to be concentrated near the areas of hydrothermal activity forming tight clusters at depths shallower than 4 km relative locations calculated using the double difference method and utilising catalogue and cross correlation differential traveltimes showed insignificant differences when compared to the nonlinear probabilistic locations in general seismicity in the tvg area seems to be primarily driven by circulation of hydrothermal fluids as indicated by the occurrence of spasmodic bursts mixed low frequency events and a b value 1 17 0 1 higher than in any other part of taiwan these observations that are similar to those reported in other dormant quaternary volcanoes indicate that a magma chamber may still exist beneath tvg and that a future eruption or period of unrest should not be considered unlikely

neoproterozoic a type magmatism in the western sierras pampeanas argentina evidence for rodinia break up along a proto iapetus rift a type orthogneisses of mid neoproterozoic age 774 6 ma u pb shrimp zircon age are reported for the first time from the grenvillian basement of the western sierras pampeanas in argentina these anorogenic meta igneous rocks represent the latest event of rodinia break up so far recognized in grenvillian basement exposures across andean south america moreover they compare well with a type granitoids and volcanic rocks along the appalachian margin of laurentia blue ridge thus adding to former evidence that the western sierras pampeanas grenvillian basement was left on the conjugate rifted margin of eastern laurentia during rodinia break up and the consequent opening of the iapetus ocean

zircon u pb chronology and elemental and sr nd hf isotope geochemistry of two triassic a type granites in south china implication for petrogenesis and indosinian transtensional tectonism abstract a detailed study utilizing zircon u pb dating major and trace element geochemistry and sr nd hf isotope geochemistry has been carried out for the caijiang granite in jiangxi province and the gaoxi granite in fujian province south china the new data indicate that the caijiang and gaoxi granites are triassic 228 230 ma and have the petrographic and geochemical characteristics of a type granites in both granites biotite occurs along the boundary of euhedral plagioclase and quartz which implies that the primary magma could have been anhydrous the two granites show high contents of total alkalis na 2 o k 2 o 7 81 12 15 high field strength elements e g zr 240 458 ppm y 16 8 38 0 ppm nb 13 5 33 8 ppm and zr nb ce y 382 604 ppm and rare earth elements total ree 211 373 ppm as well as high ga al ratios 10000 ga al 2 41 3 53 the lowest magmatic temperatures estimated from zircon saturation thermometer were 800 840 c for the caijiang granite and 820 850 c for the gaoxi granite respectively the caijiang granite has relatively high 87 sr 86 sr i ratios of 0 71288 to 0 72009 low e nd t values of 9 9 to 9 3 and low zircon e hf t values peak value of 7 5 whole rock nd isotopic model ages and zircon hf isotopic model ages mostly vary from 1 65 ga to 1 80 ga the gaoxi granite has also high 87 sr 86 sr i ratios of 0 71252 to 0 71356 low e nd t value of 13 8 and low zircon e hf t values peak value of 12 0 whole rock nd isotopic model ages and zircon hf isotopic model ages mostly vary from 1 95 ga to 2 10 ga according to these data we suggest that the two granites might have been derived from partial melting of precambrian crustal rocks that had been granulitized during an earlier thermal event our study of the caijiang and gaoxi granites together with previous studies on two triassic alkaline syenites tieshan and yangfang in fujian province and one a type granite wengshan in zhejiang province in south china indicate a wide transtensional tectonic environment in the cathaysia block that lasted at least from 254 ma to 225 ma combined with extant data for the indosinian granites and tectonic evolution in south china we suggest that the formation of a type granites was related to the local ne trending extensional faults probably caused by collision between the south china block and the indochina block or the north china block

upwelling asthenosphere beneath western arabia and its regional implications two distinct phases of continental magmatism are evident in western arabia the first from about 30 to 20 ma produced tholeiitic to transitional lavas emplaced along nw trends the second from about 12 ma to recent produced transitional to strongly alkalic lavas emplaced along n s trends the older phase is attributed to passive mantle upwelling during extension of the red sea basin whereas the younger phase is attributed to active mantle upwelling but was facilitated by minor continental extension perpendicular to plate collision the younger magmatic phase is largely contemporaneous with a major period of crustal uplift to produce the west arabian swell after about 14 ma a variety of evidence suggests that the west arabian swell is thermally supported by hot upwelling asthenosphere in contrast to the distinct asymmetry of uplift and magmatism on opposing sides of the red sea basin these processes were symmetric across a n s line marking the central axis of the west arabian swell this axis coincides with two fundamental features the ha il rutbah arch in the north and the makkah madinah nafud mmn volcanic line in the south the symmetry of magmatism is demonstrated by petrochemical evidence that the mmn harrats were derived by greater degrees of partial melting at shallower depths than those harrats lying to the west and east of the mmn line the potential temperature of the asthenosphere is estimated to be about 1436 c beneath the mmn line and about 1354 c beneath the flanking more undersaturated harrats the source of upwelling is either a mantle plume centrally located beneath the west arabian swell or an elongated and extended lobe of hot asthenosphere emanating from the ethiopian mantle plume convective flow may have been channelled along a preexisting regional flexure in the continental lithosphere which concentrated hot asthenosphere beneath the central axis of the afroarabian dome this crest of mantle upwelling underlies the mmn line in the north and the danakil depression and ethiopian rift system in the south it also passes through the red sea basin at the midpoint of an unusual doubly propagating rift system where axial seafloor spreading began 4 5 m y ago the nw trend of the red sea basin was well established by crustal attenuation during the older magmatic phase the pliocene invasion of this basin by a n s zone of mantle upwelling has resulted in seafloor spreading parallel to the preexisting structure along a rift system that has continued to propagate away from its eccentric mantle source in two opposing directions

seismicity and seismic hazard parameters evaluation in the island of crete and the surrounding area inferred from mixed data files abstract a study of the spatial distribution of seismicity and seismic hazard is undertaken for crete and the surrounding area cisa for the estimation of seismicity parameters cisa is divided in rectangular subregions by applying the centroid of strain energy technique we obtain seismicity parameter maps closely related to the tectonics of the area the b value from the magnitude frequency distribution is calculated by a maximum likelihood technique page 1968 bull seism soc am 58 1131 1168 as well as by gumbel s first asymptotic distribution of extreme values technique the b value shows consistent spatial variation along cisa for both techniques low b values are dominant in the western part of cisa while higher b values are present to the east side forming a pattern like a sleeping letter s this pattern may be attributed to the variation of the regional velocity of deformation finally we performed seismic hazard analysis for shallow and intermediate events from mixed historical and instrumental data files we estimated the regional maximum magnitude mmax as well as the other parameters like the activity rate of seismic events and the well known b parameter kijko and sellevoll 1989 bull seismol soc am 79 645 654

origin of cretaceous aluminous and peralkaline a type granitoids in northeastern fujian coastal region of southeastern china abstract in this work we report the geochemical whole rock sr nd and hf isotopes and zircon u pb age and hf o isotopic compositions for six granitic intrusions in northeastern fujian coastal region of southeastern china to elucidate the petrogenesis of aluminous and peralkaline a type granites in this region zircon u pb dating of these rocks including porphyritic syenites porphyritic granites alkali feldspar granites and arfvedsonite granites yielded late cretaceous ages of 94 98 ma mineral assemblage and geochemical features suggested that the arfvedsonite granites were peralkaline a type but the porphyritic syenites porphyritic granites and alkali feldspar granites were aluminous a type geochemical data whole rock nd hf isotopes end t 5 5 to 4 0 ehf t 3 6 to 0 and the zircon hf o isotopes ehf t 3 0 to 1 4 18o 5 4 6 0 indicated that the porphyritic syenites were produced by partial melting of crustal rocks in the lower crust the porphyritic granites and alkali feldspar granites had similar geochemical features and zircon hf o isotopic composition with the porphyritic syenites suggesting that they were formed by feldspar dominant crystal fractionation of deep crust derived syenitic magma under shallow crustal level compared with the aluminous a type granites the peralkaline a type granites had lower abundance of al2o3 mgo cao ba and sr higher abundance of sio2 and hfse as well as higher ratio of total feo mgo ga al and rb sr however the whole rock nd hf and zircon hf o isotopic compositions of the peralkaline and aluminous a type granites were similar it could be inferred that the peralkaline a type granites were formed by crystal fractionation of aluminous a type granitic magmas since the studied a type granitic intrusions were coeval with the bimodal volcanic rocks and the extensional basins in the coastal region of southeastern china they were likely produced in an extensional setting possibly during lithospheric thinning that resulted from the subduction of the paleo pacific plate beneath southeastern china

runoff generation rill erosion and time scales for hyper arid abandoned alluvial surfaces the negev desert israel abstract sequences of abandoned alluvial surfaces are ubiquitous desert landscapes considered as responding to quaternary timescale climatic fluctuations and tectonic activity the post depositional evolution surficial properties of these alluvial surfaces change with time a surface clast breakdown and development of desert pavement b dust and salts accumulation c reg gravelly desert soil evolution in the present study we focus on the hydrological response and the resulting erosional processes to these changes in surface properties over a sequence of late pleistocene holocene abandoned alluvial surfaces in nahal evrona catchment at the hyperarid southern arava valley north of the towns of eilat israel and aqaba jordan the methods used in the study are a simulated rainfall experiments to determine hydrological characteristics b terrestrial laser scanning tls to determine surface roughness c osl dating for the chronology d surface and soil descriptions and measurements and grain size analyses to determine texture of the uppermost av horizon of the reg soil e gis analysis of the new drainage network developing over the older abandoned alluvial surfaces the results show that with time roughness decreases infiltration decreases to about 8 9 relative to present rates point runoff generation increases 5 fold and as a result rill and gully erosion initiated finally leading to the destruction of the alluvial surface under the current hyper arid climate in the southern negev desert between 30 and 50 ka of surface weathering and soil development are required before significant runoff is generated and 100 ka until effective runoff initiates rill and gully erosion over these abandoned alluvial surfaces this local source runoff and gully erosion essentially destroys the alluvial surfaces in the southern arava valley within a period of 400 500 ka roughness extracted from spaceborne lidar scanning which is inversely related to surface age directly reduces friction and resistance to runoff can provide an estimate for the hydrological characteristics of the surfaces this can support applications such as rainfall runoff models risk assessment etc

a type granitoids from the eastern pontides ne turkey records for generation of hybrid a type rocks in a subduction related environment the eastern pontides is characterized by the many of intrusive bodies formed throughout the late mesozoic early cenozoic most of these are i type granitoids but here we present for the first time an a type pluton from the region to assess source characteristics and geodynamic implications the a type pirnalli pluton has a shrimp zircon u pb age of 81 2 1 ma it is composed of granite syenite and quartz monzonite and its enclaves are monzonitic in composition with elevated ga al ratios and low mg 42 the pluton is dominantly metaluminous a cnk 0 88 to 1 00 and belong to shoshonitic and ultra potassic series the samples are highly enriched in lree and show significant negative eu eu eu 0 33 to 0 92 ba nb sr and ti anomalies in the spidergrams the host rocks and their enclaves posses quite similar sr nd isotopic compositions isr 0 70693 to 0 70736 end 81 ma 2 6 to 2 0 tdm 0 94 to 1 12 ga pointing to a lower crustal parental magma with a minor contribution of lithospheric mantle we hypothesize that upwelling of asthenosphere triggered melting of chemically enriched upper mantle and basic magma formed melting of lower crust was provided by the underplating of this basic magma mixing between lower crust and mantle derived melts at depths of lower crust appears to be most reasonable petrogenetic process responsible for generation of the pluton sr nd isotope modeling suggests mixing of 82 90 of the lower crustal derived melt with 10 18 of the mantle derived melt then the hybrid melt ascended to shallower crustal level and underwent a limited fractionation process to generate a variety of rock types our data also suggest that the a type pirnalli pluton likely formed at an extensional environment of active continental margin throughout the late cretaceous ongoing extension then led to opening of black sea as a back arc basin further north of the eastern pontides

seismic characteristics and seismic hazard assessment source region of the 2015 nepal earthquake mw 7 8 in central himalaya seismicity and seismic characteristics like b value fractal dimension energy release and recurrence period are assessed for the region 80 e 89 e and 26 n 31 n which includes the 2015 large nepal earthquake mw 7 8 in central himalaya the international seismological centre isc catalogue of earthquakes with mb 3 8 for the period august 1964 january 2013 are used the b values are estimated using the maximum likelihood and least square methods the fractal dimension is estimated using the correlation integral method the events are also used for estimating radiated energy in the region the probability of occurrence of moderate earthquakes mb 5 0 using isc data and mw 6 0 using usgs data for the period 1964 2015 during a specified interval of time is estimated on the basis of three probabilistic models namely weibull gamma and lognormal the model parameters are estimated by the maximum likelihood estimates it is found that there is a 99 probability for occurrence of at least one earthquake mb 5 0 in this region in a time window of 2 3 years from the year 2013 and in 20 30 years for an earthquake mw 6 0 from the year 2015 the b value maps identified variable stressed zones and the fractal dimension maps fractal characteristics of the active fault zones the energy release map identified the zones of higher and lower energy release the percent probability maps prepared using the poisson distribution identify the zones of higher and lower probability earthquakes and thus indicate the areas of future probable earthquakes

early permian a type granites from central inner mongolia north china magmatic tracer of post collisional tectonics and oceanic crustal recycling abstract a type granitoids constitute volumetrically minor but genetically important building blocks of most post archean continental landmasses on earth and their diversified genesis encapsulates key information for ascertaining critical geodynamic controls on continental crustal formation and differentiation this zircon u pb dating and geochemical study documents the early permian peralkaline granites from central inner mongolia of china eastern central asian orogenic belt caob these granites show an a type magmatic affinity with typical enrichment in alkalis ga zr nb and y depletion in sr and p and fractionated ree patterns showing strong negative eu anomalies they have meaningful initial 87 sr 86 sr ratio of 0 70594 e nd t of 4 25 to 6 05 zircon e hf t from 9 8 to 16 0 and 18 o values from 2 41 to 4 72 these elemental and isotopic characters argue for parental magmas from partial melting of a newly trapped charnockitic lower crustal protolith and their subsequent fractional crystallization with an inherent hydrothermally altered oceanic crustal heritage and possible tectonic linkage to post collisional slab breakoff this kind of a type granites could not only serve as an insightful temporal milestone for monitoring the amalgamation between various constituent terranes in the caob but also present a spatial magmatic proxy for marking the maturation stage of juvenile crustal reworking during the final phase of a large orogenic event

early paleoproterozoic magmatism in the yangtze block evidence from zircon u pb ages sr nd hf isotopes and geochemistry of ca 2 3 ga and 2 1 ga granitic rocks in the phan si pan complex north vietnam abstract our understanding of the early evolution of the yangtze block is limited by the sparsely dispersed nature of pre neoproterozoic exposures new integrated petrographic zircon u pb age and hf nd isotope analyses and whole rock geochemical data for early paleoproterozoic granites in the phan si pan complex provides new insights into the evolution of the yangtze block as well as its role in the pre nuna supercontinent la icp ms zircon u pb dating of magmatic zircons from quartz monzonite and gneissic granite yielded 207pb 206pb ages of 2306 12 ma and 2096 15 ma respectively zircons from the quartz monzonite have ehf t values ranging from 4 1 to 2 1 corresponding to tdm2 model ages of 3002 2890 ma whereas zircons in the gneissic granite have ehf t values between 0 95 and 1 72 and corresponding tdm2 model ages of 2660 2516 ma which are consistent with their whole rock nd isotope values geochemically the quartz monzonites are i type granites combined with their relatively high sr y ratios and low y concentrations as well as fractionated ree patterns with relatively high lree but low hree concentrations they were probably generated by partial melting of the thickened middle lower crust under elevated temperature geochemical and isotopic signatures suggest that the ca 2 1 ga gneissic granites are high k calc alkaline ferroan a type granites formed by partial melting of juvenile crustal source at high temperature and low pressure with little involvement of ancient crustal material the phan si pan complex has a distinct early paleoproterozoic crustal evolution history compared with the other crustal provinces of the yangtze block suggesting independent histories that were not unified until the late paleoproterozoic during the assembly of nuna moreover the magmatism and tectonic evolution of the north vietnam region is broadly similar to that of the arrowsmith orogen of the rae craton in laurentia suggesting a potential spatial linkage the geologic record of the yangtze block does not support an early paleoproterozoic shutdown of plate tectonics

quantifying the seismicity on taiwan summary we quantify the seismicity on the island of taiwan using the frequency magnitude statistics of earthquakes since 1900 a break in gutenberg richter scaling for large earthquakes in global seismicity has been observed this break is also observed in our taiwan study the seismic data from the central weather bureau seismic network are in good agreement with the gutenberg richter relation taking b 1 when m 8 earthquake in the study region about every 25 yr however our analysis shows a lower frequency of occurrence of large earthquakes so that the expected frequency of m 8 earthquakes is about 200 yr the level of seismicity for smaller earthquakes on taiwan is about 12 times greater than in southern california and the possibility of a m 9 earthquake north or south of taiwan cannot be ruled out in light of the fukushima japan nuclear disaster we also discuss the implications of our study for the three operating nuclear power plants on the coast of taiwan

geochemical diagenetic trends during phosphorite formation economic implications the case of the negev campanian phosphorites southern israel research on the upper campanian upper cretaceous negev phosphorites mishash formation based on microprobe analyses fourier transform infrared spectroscopy wet chemistry microtextural scanning electron microscopy studies and mineralogical analyses together with quantified rates of sedimentation and p accumulation enables the chemistry of these rocks to be better constrained across the negev area and allows their suitability for the manufacture of p fertilizers to be better determined two phosphorite facies are differentiated i a pristine phosphorite facies of low p content more typical of basinal sections and ii a reworked granular phosphorite facies commonly enriched in p found predominantly near palaeo highs and forming most of the economic phosphates the distribution of f p2o5 co2 f u iv cd zn and other trace metals mo ni cr cu v and y rare earth elements concentration ce and eu anomalies and heavy rare earth elements enrichment are controlled by these two facies f p2o5 in carbonate fluorapatite is much lower 0 090 to 0 107 in the pristine than in the reworked facies 0 107 to 0 120 in addition the lower f p2o5 in the pristine facies is coupled with i higher cd zn mo ni cr cu and v concentrations ii a considerably reduced 10 u iv fraction of total u iii lower rare earth elements p2o5 and y p2o5 ratios iv less negative ce and eu anomalies and lower heavy rare earth elements lu la enrichment v an increase in fe rich smectites in the clay fraction and vi presence of oh in the carbonate fluorapatite structure sedimentary reworking of previously formed pristine phosphate together with its redeposition near structural highs in more oxic bottom conditions results in considerable diagenetic changes in the chemistry of the phosphorites making them more suitable for economic exploitation the results presented here provide geochemical criteria for identifying pristine phosphate in other phosphorite sequences and may help to better locate phosphate strata chemically suitable for the phosphate industry elsewhere

partition coefficients of hf zr and ree between zircon apatite and liquid concentration ratios of hf zr and ree between zircon apatite and liquid were determined for three igneous compositions two andesites and a diorite the concentration ratios of these elements between zircon and corresponding liquid can approximate the partition coefficient although the concentration ratios between apatite and andesite groundmass can be considered as partition coefficients those for the apatite in the diorite may deviate from the partition coefficients the hree partition coefficients between zircon and liquid are very large 100 for er to 500 for lu and the hf partition coefficient is even larger the ree partition coefficients between apatite and liquid are convex upward and large d 10 100 whereas the hf and zr partition coefficients are less than 1 the large differences between partition coefficients of lu and hf for zircon liquid and for apatite liquid are confirmed these partition coefficients are useful for petrogenetic models involving zircon and apatite

early mesozoic alkaline complexes in the northern north china craton implications for cratonic lithospheric destruction abstract early mesozoic alkaline intrusive complexes are widespread in the northern north china craton ncc and constitute an e w trending alkaline magmatic belt that is more than 1500 km long along the northern sino korean craton our new zircon and baddeleyite u pb dating results of the yongfucun yaojiazhuang and sungezhuang alkaline complexes combined with previous geochronological data indicate emplacement of the e w trending alkaline belt in the northern ncc during the middle late triassic at around 235 220 ma geochemical and sr nd hf isotopic data suggest a common source region for the syenites pyroxene syenites and mafic rocks within the complexes they were mainly derived from a metasomatized enriched lithospheric mantle however some materials from depleted asthenospheric mantle have been involved during formation of these alkaline complexes involvement of depleted asthenospheric mantle materials indicates upwelling of the asthenospheric mantle and asthenosphere lithospheric mantle interaction in northern ncc during the early mesozoic initiation of lithospheric thinning and destruction of the northern ncc occurred in the middle late triassic which is much earlier than in other parts of the ncc during the late mesozoic delamination at the root of the subduction induced thick lithospheric mantle is likely main mechanism for the early mesozoic lithospheric thinning and destruction of the northern ncc multiple subduction of oceanic plates beneath the northern southern and eastern parts of the ncc and interactions of the surrounding orogenesis during the late paleozoic to mesozoic may play important roles on the late mesozoic lithospheric destruction of the ncc

mineral chemistry trace elements and sr nd hf isotope geochemistry and petrogenesis of cailing and furong granites and mafic enclaves from the qitianling batholith in the shi hang zone south china abstract the shi hang zone is an important ne trending mesozoic magmatic belt composed of granites with relative high end t values and young tdm model ages in south china however the petrogenesis and the tectonic environment for the shi hang zone magmatic rocks remain controversial we report here mineral chemistry geochemical and sr nd hf isotopic data for the cailing and furong granites and mafic microgranular enclaves mmes from the qitianling granite batholith in southern hunan province south china the qitianling granite batholith is a multi staged composite pluton with three phases cailing furong and huangtangling according to their ages and petrography the cailing 163 160 ma and furong 157 153 ma phases are mainly composed of porphyritic amphibole biotite monzogranite and they share similar geochemical and isotopic characteristics both of them show similar sio2 contents from 66 50 to 70 28 and metaluminous a cnk values of 0 80 to 0 98 the granites are characterized by high contents of large ion lithosphile elements lile such as rb th u pb high field strength elements hfse such as nb ta zr hf and zr nb ce y contents 350 ppm and high 10 000 ga al ratios 2 6 chondrite normalized ree patterns show relative enrichment of light rare earth elements lrees and significant negative eu anomalies mineralogical and geochemical features suggest that the cailing and furong granites are a type which can be further classified as a2 subtype they have relatively lower 87sr 86sr i ratios 0 7091 0 7132 higher end t values 5 5 to 7 6 and younger nd isotopic model ages 1 48 1 56 ga than those common s type granites in south china zircon ehf t values vary from 8 1 to 3 7 the mmes in the cailing phase show similar trace element and sr nd isotopic characteristics with the host granites but zircons from the mmes show different ehf t values 6 4 2 6 with those from the host granites 8 1 to 3 7 this indicates that the mmes and host granites were crystallized from different sources of magmas providing direct evidence for mafic felsic magma mixing processes the isotope data indicate that the cailing and furong granites from the qitianling batholith were derived from a hybrid magma consisting of about 80 felsic magma derived from old crust and about 20 mantle derived mafic magma the strong magma mixing at about 160 155 ma caused by intra arc rifting or back arc extension related to subduction of the paleo pacific plate is favored to explain the petrogenesis of the cailing and furong granites as well as the shi hang zone

multifractal measures of earthquakes in west taiwan the generalized fractal dimension for epicentral distribution of earthquakes in west taiwan is measured the entire area is first divided into two zones i e north and south zones after which the two zones are further separated into three subzones for the former and two for the latter the logc q r versus logr function wherec q r is the generalized correlation integral andr is the distance between two epicenters shows that a linear relation between logc q and logr exists in the range ofr smaller thanr c the value ofr c is 25 km for the north zone 40 km for the south and 12 km for the three north subzones the valuesr c 25 and 40 km are almost the smallest ones of the width of epicentral distributions of the north and south zones respectively the value ofr c 12 km for the three north subzones is approximately the smallest size of the cluster of epicenters for the plots of two south subzones the pattern of data points does not bend in the range ofr in consideration and thus there is not such a critical radius thed q q relations forq 0 1 2 15 are constructed for the two zones and five subzones results show significant multifractality and a spatial variation in multifractality for epicentral distributions of earthquakes in west taiwan

spatiotemporal variations in the b value of earthquake magnitude frequency distributions classification and causes abstract interpretation of the b value of earthquake frequency magnitude distributions has received considerable attention in recent decades this paper provides a comprehensive review of previous investigations of spatial and temporal variations in b value including their classification and possible causes based on least squares regression of seismicity data compiled from the neic iris and isc catalogs we find an average value of 1 02 0 03 for the whole earth and its two hemispheres consistent with the general view that in seismically active regions the long term average value is close to unity nevertheless wide ranging b variations 0 3 b 2 5 have been reported in the literature this variability has been interpreted to arise from one or more of the following factors prevailing stress state crustal heterogeneity focal depth pore pressure geothermal gradient tectonic setting petrological environmental geophysical characteristics clustering of events incomplete catalog data and or method of calculation excluding the latter all of these factors appear to be linked directly or indirectly with the effective state of stress although time dependent changes in b value are well documented conflicting observations reveal either a precursory increase or decrease in b value before major earthquakes our compilation of published analyses suggests that statistically significant b variations occur globally on various timescales including annual monthly and perhaps diurnal taken together our review suggests that b variations are most plausibly linked with changes in effective stress

genesis of silicic magmas during tertiary continental rifting in yemen abstract the magmatism in yemen associated with oligo miocene continental rifting in the red sea and the gulf of aden comprises a bimodal mafic felsic suite represented by flows dykes and plutons this paper reports the chemical and nd sr isotopic compositions of the felsic rocks trachytes syenites rhyolites and granites associated with the yemen trap series and deals with the controversy in regard to the crustal or mantle origin of a type magmas generated in tensional contexts the overall age of the studied rocks ranges from 26 5 to 16 ma the major and trace element compositions of the felsic rocks can partly be explained by fractional crystallization from some of the basic magmas this process was more extensive in the case of the rhyolites and some of the granites than that of the trachytes and the syenite in addition the trachytes differ from the rhyolites by featuring a negative nb anomaly that suggests contamination by continental crust the trachytes have much lower 143 nd 144 nd ratios and higher 87 sr 86 sr ratios than the associated basalts whereas the rhyolites have much higher 87 sr 86 sr ratios but 143 nd 144 nd ratios identical to those of the basalts the plutons span the whole compositional range of isotopic compositions displayed by the trachytes and the rhyolites the isotopic compositions of the felsic rocks do not support their genesis by direct melting of continental crust rather these rocks were generated in an open magma system that evolved by a combination of fractional crystallization and crustal contamination mixing and afc processes involving heterogeneous crust are both required to explain the trachytic and rhyolitic compositions where various amounts of crystal fractionation and crustal contamination were involved the genetic differences between the trachytes and the rhyolites are related to their respective ages the highest degree of contamination observed in the trachytes occurred contemporaneously with the emplacement of the traps and could have been related to a high thermal gradient in the crust due to massive magma transfer at that time this stage presumably corresponds to the impingement of the afar plume head against the lithosphere the less contaminated and more fractionated rhyolites which formed later during continental rifting are consistent with a lower thermal gradient

zircon u pb geochronology and geochemistry of two types of paleoproterozoic granitoids from the southeastern margin of the north china craton constraints on petrogenesis and tectonic significance abstract two types of paleoproterozoic granitoids i e k feldspar albite granites and granitic gneisses were recognized from the wuhe complex of the precambrian basement and neighboring areas in the southeastern margin of the north china craton ncc they share the identical 207pb 206pb ages of 2096 9 ma and 2096 8 ma defined by zircon shrimp u pb dating these granitic rocks are commonly enriched in hree zr nb ga and y and depleted in v cr and ni most of which have high tfeo mgo ratios and zr saturation temperatures over 850 c suggestive of an affinity with a type granite in addition both have consistent whole rock end t values 3 0 to 0 9 and zircon hf isotopic compositions ehf t 3 3 to 1 9 the latter are similar with ones of the neoarchean ttg gneisses in the eastern block of the ncc thus these 2 1 ga granitoids in the region were most likely derived from the partial melting of 2 5 ga ttg gneisses with minor involvement of coeval mafic crustal materials the zircon grains from the granitic gneisses can be categorized into core mantle and rim domains with distinct cl images and trace element characteristics the grey mantles exhibit steep ree patterns low lree th pb contents and remarkably low th u ratios

estimates of earthquake recurrences in the chiayi tainan area taiwan abstract in the light of the important role played by the return period in seismic hazard analysis two types of statistical analyses gutenburg richter s law and markov chain were applied to study the earthquake periodicity in the chiayi tainan area there are two data sets prepared for this study one contains earthquakes with ml 4 283 events during the 1900 1995 period the other contains earthquakes with ml 2 3816 events during the 1973 1995 period the mean return period and b values estimated with gutenburg richter relation for earthquakes in the study area are in agreement with previous studies the mean return period for ml 6 earthquakes is 9 7 years from the data in 1900 1995 period and 17 years from the data in 1900 1995 period the markov chain measures the transition characteristics of earthquakes and estimates that ml 6 6 9 and ml 7 0 earthquakes repeat at intervals of 28 and 135 of ml 4 earthquake events respectively in the chiayi tainan area this study also demonstrated that investigation of substitutability phenomenon is applicable to earthquake data which suggests high similarity for low magnitude earthquakes and dissimilarity for high magnitude earthquakes the result from these statistical approaches for earthquake occurrences leads to a conceptual model inferring fault behavior this model is supported by the recent geologic findings which may be potentially useful in earthquake hazard assessment

seismotectonics of taiwan abstract high quality seismicity data and focal mechanism solutions obtained during 1973 1983 by the permanent taiwan telemetered seismographic network and several temporary local seismographic networks are used for a detailed study of the seismotectonics of the taiwan area seismicity distribution in southern taiwan clearly reveals an east dipping benioff zone which has a thickness of about 30 km and begins to deepen along 121 e at a dip angle of 55 60 the leading edge of this benioff zone reaches a depth of about 180 km between 21 n and 22 n but tapers off to a shallower depth of about 100 km from 22 n to 23 n the presence of this seismic zone implies that subduction of the south china sea plate under the philippine sea plate extends from luzon northward to about 23 n the position of the northern boundary of the south china sea plate as tentatively defined according to the seismicity distribution passes through southern taiwan from the offshore area in the taiwan strait west of kaohsiung in an east northeast direction to the taitung area where a triple junction probably lies seismicity is found to disappear abruptly below a certain depth in many parts of taiwan this phenomenon may be attributed to the frictional to quasiplastic transition in the crust or upper mantle comparison of shallow seismicity with surface faults and fractures shows that all areas of active shallow seismicity are marked by densely developed faults and fractures however the converse is not necessarily true this may be partly due to the relatively short duration of seismicity data and partly due to excessive weakening of some of the severely faulted and fractured areas finally focal mechanism solutions for west central taiwan and the kuangfu fuli area in eastern taiwan predominantly show a maximum horizontal compression in the se nw direction which can be related to collision between the eurasian and philippine sea plates however focal mechanism solutions for both the hualien area in eastern taiwan and the tainan area in southwestern taiwan show remarkable irregularities which may result from local tectonic complexities

the rare earth element ree mineralisation potential of highly fractionated rhyolites a potential low grade bulk tonnage source of critical metals abstract the rare earth elements ree have become crucial for modern industry technology and medicine with the increase in demand for these elements over the past few years currently being met by relatively few well known mineral deposits this lack of a secure supply of the ree has led to increased research into potential alternative sources of these in demand elements the primary fractionation processes involved in the petrogenesis of highly fractionated high silica rhyolites can cause the magmas that form these units to become preferentially enriched in the ree especially in the more valuable heavy ree hree although this is dependent on the mineral assemblages fractionated by the system in question a factor that is in turn a function of the source and tectonic setting of a given magmatic event the mineralogy of the ree is also important with volatile exsolution and vapour phase activity within highly evolved rhyolite systems potentially having a key role in concentrating the ree and other elements into concentrations and more importantly potentially acid leachable and therefore processable minerals that may be economically viable to extract this combined with the fact these rhyolites are often enriched in other critical and or economically important metals e g y nb ta be li f sn rb th and u means that these volcanic units should be considered as potential sources of these critical metals in addition the large volume nature of these rhyolites combined with the fact they frequently crop out at the earth s surface makes them ideally suited for more economical bulk open pit extraction this suggests that these high silica ree enriched rhyolites should be considered potential ree analogues of bulk tonnage low grade porphyry cu deposits warranting further investigation to determine whether these rhyolites are a viable new source of the ree especially the hree and are potential targets for future mineral exploration

geochemistry of miocene trachytes in bugasi lhasa block tibetan plateau mixing products between mantle and crust derived melts abstract it is generally believed that cenozoic potassic and ultrapotassic volcanic rocks of the tibetan plateau were generated by partial melting of an enriched mantle region or lower crustal materials the miocene bugasi volcanic rocks bvr in the western part of the lhasa block are composed mainly of trachyandesites and trachytes both of which belong to the shoshonite series the trachytes show somewhat transitional compositions between the mantle derived trachyandesites of the bvr and the crust derived potassic rocks of konglongxiang most evident in their sr ba and ni concentrations nb ta rb sr th nb zr nb and ba rb trace element ratios and sr and nd isotopic compositions these features coupled with the relatively high cr and ni concentrations and mg suggest that the trachytes are the product of mixing between mantle derived and lower crust derived melts

petrogenesis of permian a type granitoids in the cihai iron ore district eastern tianshan nw china constraints on the timing of iron mineralization and implications for a non plume tectonic setting abstract the geochronology and geochemistry of granitoids in the eastern tianshan nw china provide important constraints on the timing of iron mineralization as well as in understanding evolution history of the southern central asian orogenic belt caob here we present results from a detailed study on granitoid rocks from the cihai iron ore district in the beishan region southern part of the eastern tianshan the granitoid rocks are composed of granodiorite quartz monzonite granite and monzonite zircon u pb analyses yielded the ages of 294 1 2 2 ma 286 5 0 7 ma 284 3 3 3 ma and 265 6 3 0 ma respectively suggesting they were formed in early middle permian among these granitoid rocks the ages of quartz monzonite and granite are close to the timing of iron mineralization 282 ma indicating they may provide a source of iron in the cihai ore district geochemically the granodiorite granite and quartz monzonite samples are characterized by high feo t feo t mgo and ga al ratios 0 84 0 94 and 2 28 3 27 respectively as well as high zircon saturation temperatures 781 908 c similar to those of typical a type granitoids isotopically they display consistently depleted hf isotopic compositions e hf t 1 18 to 15 37 geological geochemical and isotopic data suggest that the cihai a type granitoids were derived from melting of juvenile lower crust some early permian a type granitoids were recently identified in the tarim and eastern tianshan with the ages between 294 and 269 ma the a type granitoids in the eastern tianshan formed earlier between 294 284 ma and exhibit characteristics of a 2 type granitoids whereas the a type granitoids in the tarim formed later between 277 269 ma and show a 1 granitoids affinity we suggest that the permian tarim mantle plume does not account for the formation of the a type granitoids in the eastern tianshan area and the eastern tianshan was in a non plume tectonic setting during early permian time a slab break off event has been suggested as the possible tectonic mechanism that triggered the formation of early permian a type granitoids in the eastern tianshan

landslide seismic magnitude abstract landslides have become one of the most deadly natural disasters on earth not only due to a significant increase in extreme climate change caused by global warming but also rapid economic development in topographic relief areas how to detect landslides using a real time system has become an important question for reducing possible landslide impacts on human society however traditional detection of landslides either through direct surveys in the field or remote sensing images obtained via aircraft or satellites is highly time consuming here we analyze very long period seismic signals 20 50 s generated by large landslides such as typhoon morakot which passed though taiwan in august 2009 in addition to successfully locating 109 large landslides we define landslide seismic magnitude based on an empirical formula lm log a 0 55 log 2 44 where a is the maximum displacement m recorded at one seismic station and is its distance km from the landslide we conclude that both the location and seismic magnitude of large landslides can be rapidly estimated from broadband seismic networks for both academic and applied purposes similar to earthquake monitoring we suggest a real time algorithm be set up for routine monitoring of landslides in places where they pose a frequent threat

temporal changes in the cumulative piecewise gradient of a variant of the gutenberg richter relationship and the imminence of extreme events abstract it is generally found that the relative frequencies of occurrence of earthquakes of different magnitudes in seismogenic zones have a power law distribution for a long term dataset the overall slope of this logarithmically transformed distribution is usually indicated by a best fit straight line and expressed as a b value this slope is stable and normally lies between 0 8 and 1 2 the actual value depending on the region examined and the threshold selected for data completeness the linearity of the distribution can be used to make statistical inferences about the potential for larger events over the long run and with appropriate reservations may even be extrapolated to magnitudes that are beyond recent experience we suggest the same information can also be viewed over shorter intervals in terms of an empirical piecewise distribution with relative frequencies of occurrence at adjacent magnitude steps controlling the local slope of the distribution an emergence through time of an excess number of lower magnitude earthquakes causes temporal changes to appear in the low end piecewise gradients of this distribution a marked excursion away from an overall uniform trend for the particular zone may be indicative of an imminent larger event on two separate occasions in 1982 and 1997 such temporal variations were seen in the magnitude distributions of sequences of events near tobago west indies and used to anticipate subsequent damaging mainshocks the recognition of temporal departures from overall linearity of the magnitude frequency relation in a suitable dataset may thus provide an evidential element that can contribute to earthquake forecasting this phenomenological approach was used in the analysis of the neic global dataset of earthquakes of magnitude 6 1 and bigger for the period 1973 2003 to explore its wider applicability trends in the piecewise gradients of the global data were interpreted as pointing to an imminent great earthquake perhaps exceeding magnitude 8 5 such an event did occur shortly afterwards in the form of the great sumatran earthquake of 2004 12 26 following that event global magnitude production continued to exhibit sharp imbalances in the lower magnitude bins indicating that another similar event was likely the second sumatran earthquake on 2005 03 28 satisfied that projection since that time a magnitude production imbalance persists in the global dataset suggesting the system could be poised to output an earthquake or earthquakes in the magnitude range 8 6 9 0 or even greater this contribution describes the piecewise gradient approach and examines its application to global earthquake data

petrogenesis of a type granitoids from the alto moxoto and alto pajeu terranes of the borborema province ne brazil constraints from geochemistry and isotopic composition abstract a type granitoids 512 ma either intruded into paleoproterozoic gneiss of the alto moxoto terrane prata complex and serra da engabelada pluton or into early neoproterozoic metavolcanic metasedimentary sequence of the alto pajeu terrane serrote santo antonio pluton constitute a small proportion of brasiliano pan african granitoids in the central tectonic domain of the borborema province northeastern brazil the prata complex consists of syenogranites monzogranites mafic enclaves of diorites and norites the felsic and mafic members are not genetically related through fractionation mingling and mixing were extensive processes within the prata complex the granites evolution appears to have involved fractionation of alkali feldspar biotite apatite and sphene without significant wall rock assimilation the serra da engabelada and serrote santo antonio plutons consist of biotite syenogranites with rare mafic enclaves the studied granitoids are dominantly metaluminous characterized by fe rich biotite and fe hornblende high total alkalis y nb and ree and low cao mgo and sr abundances and high feo feo mgo ratios characterize these granitoids chondrite normalized ree patterns show enriched lree moderate to strong negative eu anomalies and more or less flat heavy ree the studied granitoids and diabase from dykes and enclaves show negative end 512ma values 14 to 10 high incompatible elements such as lile hfse and ree suggesting important contribution of paleoproterozoic crust the origin of the granites is thought to have involved partial melting of granodioritic or tonalitic lower crust such isotopic signature of the diabase from the dykes also reflects a paleoproterozoic enriched lithospheric mantle in the area the intrusion of the studied granitoids contemporary with sub volcanic bimodal magmatism and deposition of many cambrian pull apart basins in the north and central tectonic domain of the borborema province suggest intrusion during post tectonic relaxation of the brasiliano orogeny following the assembly of west gondwana

the seismic parameter b of the frequency magnitude relation and its association with the geological zones in the area of greece abstract the parameter b of the frequency magnitude relation has been accurately calculated for each of the 21 seismic zones into which the aegean and surrounding area 34 n 43 n 18 e 30 e has been divided on the basis of several seismotectonic criteria these 21 seismic zones have been geographically separated into three a b c groups regions according to the values of the parameter b the outer region a is characterized by a relatively high value 1 03 the middle region b by an intermediate value 0 84 and the innermost region c by a low value 0 60 the boundaries of these three groups of zones almost coincide with the boundaries of well known geological zones this observation is interpreted in terms of mechanical heterogeneity of the material and of structural and stress conditions in the area

formation and stabilization of the dunhuang block nw china constraints from the late paleoproterozoic a type granites of the dunhuang complex abstract the geochemical composition and temporal evolution of a type granites may hold key information regarding critical geodynamic processes that occurred during the evolution of the continental crust moreover these aspects may provide an indication of when orogenic processes ended and craton formation stabilization began in early precambrian blocks in this study we report the results of zircon u pb ages hf isotope data and whole rock geochemistry for the proterozoic huoyanshan potassic granites in the dunhuang block northwest china zircon u pb dating reveals that the huoyanshan granites were emplaced at ca 1791 1786 ma representing a late paleoproterozoic magmatism event the granites have high sio2 70 71 72 20 wt total alkali contents k2o na2o 8 81 8 96 wt k2o na2o 1 57 1 66 tio2 mgo ratios 2 19 2 57 low cao 0 77 1 27 wt mgo contents 0 12 0 16 wt and mg values 7 72 8 67 with a cnk ratios of 0 96 1 04 pointing to alkaline and metaluminous to weakly peraluminous affinities these granites are characterized by high total rare earth element concentrations ree 419 755 ppm and variable la yb n values 8 24 with significantly negative eu anomalies eu eu 0 31 0 42 the primitive mantle normalized trace element patterns suggest that the huoyanshan plutons are depleted in ba nb ta sr p and ti but enriched in rb th and pb additionally the granites have a high zirconium saturation temperature of 855 897 c with an average of 878 c these geochemical characteristics indicate that huoyanshan potassic granites are an aluminous a type granite and further classified as a2 type together with the zircon hf isotope data ehf t 11 21 to 2 76 indicates that these granites were generated from a crustal source the heterogeneous hf isotope compositions in zircons are principally caused by the disequilibrium melting of zr bearing sources in addition two stage hf model ages of zircons from the granites are ca 2 6 3 1 ga and plot on the average crustal evolution trend of archean tonalite trondhjemite granodiorite ttg gneiss 2 5 to 3 0 ga in the dunhuang block thus we propose that a type granites in the study area were generated from the disequilibrium partial melting of archean tonalitic to granodioritic rocks under high temperature and low pressure conditions according to their low al2o3 cao na2o k2o molar values and high 10000 ga al values 2 9 subsequently the magma experienced prominent fractional crystallization of k feldspar plagioclase orthopyroxene and or magnetite our results with available data suggest that the huoyanshan granites formed in a tectonic transform regime within a collisional to extensional setting and serve as a precursor for the formation and stabilization of the dunhuang block during the late paleoproterozoic furthermore it is probable that the post collisional magmatism event at ca 1 79 ga in the dunhuang block was closely related to the assembly of the columbia supercontinent

late carboniferous bimodal volcanic rocks and coeval a type granite in the suman khad area southwest mongolia implications for the tectonic evolution abstract the volcanic rocks in the suman khad area in southwest mongolia form a bimodal suite consisting mainly of peralkaline rhyolites with subordinate basalts the rhyolite sample collected from the bimodal suite yielded a shrimp zircon u pb age of 314 5 ma mswd 1 41 n 12 which was interpreted to represent formation time of the bimodal volcanic suite the basalts were characterized by enrichment in lile and lree and depletion in hfse indicating their formation was related to subduction processes these features together with their positive end t values 6 3 6 7 suggest that the basalts were likely derived from a depleted mantle source metasomatized by subduction related fluids in various tectonic discrimination diagrams the basalts exhibited a transition from true arc basalts to intraplate basalts and thus were suggested to from in a back arc tectonic setting the rhyolites show a close affinity to a type granites with enrichment in lile and lree depletion in nb ta and ti and positive end t values 6 0 6 4 considering the observed distinct compositional gap between the endmembers of the bimodal suite the rhyolites are proposed to originate from partial melting of juvenile basaltic crustal rocks rather than fractional crystallization of basaltic melt the granite associated with the bimodal volcanic rocks yielded a shrimp zircon u pb ages of 312 5 ma mswd 0 75 n 13 indicating that the granite is contemporaneous with the bimodal volcanic suite the granite samples showed typical a type granitic geochemical affinities and are considered to have been formed by partial melting of crustal rocks in a within plate tectonic setting based on a combination of the available data we suggest that the late carboniferous bimodal volcanic suite together with the coeval a type granites in the suman khad region probably document a back arc basin extensional environment which probably related to the roll back of the paleo asian oceanic plate during the northward subduction under the central mongolia microcontinent

petrogenesis and tectonic setting of the tuyeh darvar granitoid northern iran constraints from zircon u pb geochronology and sr nd isotope geochemistry abstract tuyeh darvar granitoid which outcrop ca 45 km sw of damghan city in the eastern alborz zone comprise mainly the pluton emplaced into the barut formation of lower cambrian ages zircon u pb ages show carboniferous ages 325 3 ma for the formation of this granitoid the granitoid is mostly metaluminous ferroan and alkalic monzonite to monzodiorite these rocks have high values of feot mgo and ga al high concentrations of k2o na2o low abundances of mgo and transitional elements plots normalized to chondrite and primitive mantle compositions show strong enrichments of lree relative to hree and of lile relative to hfse accompannied by negative anomalies of nb and sr they contain fe rich hydrous mafic minerals and magnetite these features are typical of a type granites sr nd isotopic geochemistry with initial nd values from 1 1 to 1 5 and initial 87sr 86sr ratios between 0 70562 and 0 70678 are consistent with magmatic differentiation from mafic melts produced from an enriched mantle source however other models such as melting of mafic crust or mixing of components from depleted mantle and continental crust cannot be discarded on the basis of the u pb zircon age 325 3 ma and the known magmatic tectonic regime in iran during the paleozoic it is suggested that the pluton formed in a rift environment related to extensional structures of the alborz block in early carboniferous time

b values of two tectonic parts in the circum pacific belt two different data sets have been applied to compute theb parameter of the magnitude frequency relation for two different areas in the circum pacific belt these areas are a south america middle america and mexico b all the remaining island arcs of the circum pacific belt starting from alaska and the aleutian islands and proceeding southeastwards the first data set spreads over 77 years while the second one covers a 90 year period in both cases the results clearly showed that theb values are lower in the first of the above mentioned areas while respectively higher in the second this is due to the tectonic conditions in these areas as estimated during the present work

the taiwan telemetered seismographic network abstract in 1972 the taiwan telemetered seismographic network ttsn was installed to monitor earthquakes occurring in an area from 21 to 26 n latitude and from 119 to 123 e longitude the number of stations increased from six in 1972 to 24 in 1987 the stations are equipped with velocity type seismometers with a natural frequency of 1 hz since 1983 horizontal component sensors have been added at several stations signals recorded by the field stations are transmitted to taipei recording center through telephone lines or radio and then recorded on fm magnetic tapes paper and nine track magnetic tapes through a d converters hypocenters of earthquakes are routinely determined by a hypoc2 computer program the size of an earthquake is estimated from the signal duration moreover a simulated wood anderson seismographic station is in operation at taipei for the determination of local magnitude a seismic work system sws is being established for automatic data acquisition and data processing to avoid clipping of signal amplitude an optimum telemetry system is being linked to the ttsn

2090 2070 ma a type granitoids in zanhuang complex further evidence on a paleoproterozoic rift related tectonic regime in the trans north china orogen abstract the xuting pluton located at the north section of the zanhuang complex contains potassic and sodic granite in both of which shallow level emplacement is shown by graphic texture feldspar and quartz intergrowth two potassic granite and one sodic granite samples yielded zircon 207 pb 206 pb ages of 2066 17 ma 2092 14 ma and 2071 14 ma respectively suggesting that the xuting pluton emplaced between 2070 ma and 2090 ma which is coeval with the paleoproterozoic gantaohe group dominated by mafic volcanic and sedimentary rocks the potassic granite is enriched in sio 2 total feo rees except eu zr nb ga and y and depleted in mgo cao al 2 o 3 sr v cr and ni with high tfeo mgo ratios consistent with the features of a type granite except for the high mgo and low k 2 o contents the sodic granite also presents most of the features of a type granites the zircon saturation temperatures from the potassic and sodic granites range from 855 to 998 c and 853 to 933 c respectively indicating that they are from the high temperature magma the potassic granites have the e hf t ranging from 5 9 to 1 33 and hf model ages of 2 5 2 8 ga which are identical with the ages of neoarchean ttg gneisses in the zanhuang complex we propose that the potassic granite in the xuting pluton derived from the partial melting of neoarchean ttg gneisses the sodic granites also present negative e hf t values from 4 81 to 0 76 and hf model ages of 2 5 2 8 ga suggesting that they come from the partial melting of the neoarchean crust however with relative enrichment in mgo and total feo and lower k 2 o and rb the sodic granite was derived from a mafic source in the lower crust the likely heat source was high heatflow associated with mantle upwelling the a type xuting pluton and mafic volcanic rocks in the gantaohe group constitute a bimodal lithologic association from a paleoproterozoic continental rift environment 2 2 2 0 ga magmas are widely distributed along the trans north china orogen tnco and also present a bimodal character we propose that 2 2 2 0 ga bimodal magmas throughout the tnco were likely formed in a paleoproterozoic rifting setting considering the widespread 2 2 2 0 ga magmatic rocks in the north china craton ncc we infer that the magmatism likely occurs in tensional environment after the initial amalgamation of the ncc in the late archean

an early permian ca 280 ma silicic igneous province in the alxa block nw china a magmatic flare up triggered by a mantle plume abstract silicic igneous provinces have important implications for geodynamic processes in this study we show that the predominantly early permian ca 280 ma granitoids in the alxa block correspond to an important silicic igneous province with areal distribution in northwest nw china we present zircon u pb age and hf o isotopic and whole rock geochemical and sr nd isotopic data for the newly identified i and a type granites and high sr y granodiorites in the bayannuoergong batholith and gabbros diorites and quartz diorites in the bijiertai complex alxa block the i type monzogranites granodiorites and a type granites of the bayannuoergong batholith were probably generated by mixing between crust and mantle derived magmas partial melting of a thickened eclogitic lower crust and underplated mantle derived mafic rocks respectively the gabbros quartz diorites and diorites of the bijiertai complex were likely generated by partial melting of the lithospheric mantle differentiation from basaltic magmas and partial melting of the middle crust respectively despite pronounced geochemical and isotopic heterogeneity of these rocks new sims and la icp ms u pb zircon dating indicates that they were formed over a very short time interval at ca 280 ma thus the mantle lower crust and middle crust underwent widespread melting at this time given that these magmatic rocks have no spatial or temporal zonation and were probably formed in an extensional setting we suggest that the ca 280 ma tarim mantle plume in nw china may have triggered the magmatic flare up of the alxa silicic igneous province

revisiting early middle jurassic igneous activity in the nanling mountains south china geochemistry and implications for regional geodynamics abstract early middle jurassic igneous rocks 190 170 ma are distributed in an e w trending band within the nanling tectonic belt and have a wide range of compositions but are only present in limited volumes this scenario contrasts with the uniform but voluminous middle late jurassic igneous rocks 165 150 ma in this area the early middle jurassic rocks include oceanic island basalt oib type alkali basalts tholeiitic basalts and gabbros bimodal volcanic rocks syenites a type granites and high k calc alkaline granodiorites geochemical and isotopic data indicate that alkaline and tholeiitic basalts and syenites were derived from melting of the asthenospheric mantle with asthenosphere derived magmas mixing with variable amounts of magmas derived from melting of metasomatized lithospheric mantle in comparison a type granites in the study area were probably generated by shallow dehydration related melting of hornblende bearing continental crustal rocks that were heated by contemporaneous intrusion of mantle derived basaltic magmas and high k calc alkaline granodiorites resulted from the interaction between melts from upwelling asthenospheric mantle and the lower crust the early middle jurassic magmatic event is spatially variable in terms of lithology geochemistry and isotopic systematics this indicates that the deep mantle sources of the magmas that formed these igneous rocks were significantly heterogeneous and magmatism had a gradual decrease in the involvement of the asthenospheric mantle from west to east these variations in composition and sourcing of magmas in addition to the spatial distribution and the thermal structure of the crust mantle boundary during this magmatic event indicates that these igneous rocks formed during a period of rifting after the indosinian orogeny rather than during subduction of the paleo pacific oceanic crust

the volcanic massif of biq at hayareah sinai negev a case of potassium metasomatism on biq at hayareah an area 80 km 2 in size on the border between sinai egypt and the negev israel a sequence of late precambrian alkali rhyolites lavas tuffs and ignimbrites and their hypa byssal equivalents rhyolite porphyries are exposed these rocks form part of the alkaline katharina province representatives of which are found from the indian ocean to west africa about half the rocks of biq at hayareah have undergone a mainly metasomatic alteration not recognizable in hand specimens chemically the alteration is expressed by the almost total exchange of na by k and by the addition of about 3 silica and of a small amount of alumina the trace element composition remained almost unaffected mineralogically albite has been replaced by k feldspar and secondary quartz has crystallized while some primary quartz has been replaced by k feldspar it is concluded that the potash metasomatism is the result of an interaction between the originally partly glassy rhyolites and hyd

sr and nd isotopic compositions age and petrogenesis of a type granitoids of the vernon supersuite new jersey highlands usa abstract voluminous late mesoproterozoic monzonite through granite of the vernon supersuite underlies an area of approximately 1300 km2 in the highlands of northern new jersey the vernon supersuite consists of hastingsite biotite bearing granitoids of the byram intrusive suite bis and hedenbergite bearing granitoids of the lake hopatcong intrusive suite lhis these rocks have similar major and trace element abundances over a range of sio2 from 58 to 75 wt are metaluminous to weakly peraluminous and have a distinctive a type chemistry characterized by high contents of y nb zr lree and ga al ratios and low mgo cao sr and hree whole rock rb sr isochrons of bis granite yield an age of 1116 41 ma and initial 87 sr 86 sr ratio of 0 70389 and of lhis granite an age of 1095 9 ma and initial 87 sr 86 sr ratio of 0 70520 both suites have similar initial 143 nd 144 nd ratios of 0 511267 to 0 511345 bis and 0 511359 to 0 511395 lhis values of end are moderately high and range from 1 21 to 2 74 in the bis and 2 24 to 2 95 in the lhis petrographic evidence field relationships geochemistry and isotopic data support an interpretation of comagmatism and the derivation of both suites from a mantle derived or a juvenile lower crustal parent with little crustal assimilation both suites crystallized under overlapping conditions controlled by p t fh2o lake hopatcong magma crystallized at a liquidus temperature that approached 900 c and a pressure of about 6 kbar and remained relatively anhydrous throughout its evolution initial p t conditions of the byram magma were 850 c and about 5 5 kbar bis magma was emplaced contemporaneous with or slightly preceding lhis magma and both magmas were emplaced during a compressional tectonic event prior to granulite facies metamorphism that occurred in the highlands between 1080 and 1030 ma

geochronology elemental and nd hf isotopic geochemistry of devonian a type granites in central jiangxi south china constraints on petrogenesis and post collisional extension of the wuyi yunkai orogeny abstract details on processes of the early middle paleozoic wuyi yunkai orogeny in south china remain poorly defined most silurian devonian granites in south china are s type or i type granites which are suggested to be petrogenetically related to the wuyi yunkai orogeny this paper firstly reported a systematic study on two devonian a type granites in the central jiangxi province la icp ms zircon u pb dating results imply that the huitong and epo granites were emplaced at about 415 ma both of the two granites have the petrographic and geochemical characteristics of a type granites interstitial biotites occur along the boundary of euhedral plagioclase and quartz and they formed later than plagioclase and quartz it implies that the primary magma could have been anhydrous biotites from the two granites are fe rich and have high fe 2 fe 2 mg 2 ratios 0 60 0 74 the magmatic temperatures estimated from zircon saturation thermometer are 802 920 c for the two granites higher than common i type and s type granites the two granites show high contents of total alkalis na 2 o k 2 o 6 96 9 39 wt high field strength elements e g zr 181 437 ppm y 22 1 39 7 ppm nb 18 6 30 3 ppm and zr nb ce y 324 555 ppm rare earth elements total ree 155 312 ppm as well as high ga al ratios 10 000 ga al 2 50 3 44 these geochemical characteristics are similar to those of a type granites the huitong and epo granites have relatively low e nd t values of 10 4 to 7 7 and low zircon e hf t values peak value of 8 0 whole rock two stage nd isotopic model ages and zircon hf isotopic model ages mostly vary from 1 78 ga to 2 00 ga according to these data we suggest that the two granites might have derived from partial melting of pre cambrian sedimentary rocks which had been granulitized during an earlier thermal event the two granites contain abundant contemporaneous mafic microgranular enclaves mmes the mmes display igneous textures and contain acicular apatites suggesting quenching of mafic magmas that have co mingled with the host granites the mmes might have derived from the enriched lithospheric mantle source this study on the devonian huitong and epo a type granites together with previous studies on paleozoic granites in south china indicated that the wuyi yunkai orogeny in south china had changed from syn collisional crustal thickening to post collisional extension at least from 415 ma

a late proterozoic bimodal volcanic subvolcanic suite from wadi araba southwest jordan abstract geotectonic setting age relationships petrography and geochemistry of a pan african bimodal volcanic subvolcanic suite have been examined the volcanic phase terminated the pan african molasse evolution and spans the time interval 550 540 ma the volcanics forming a 70 km nne ssw trending belt are distributed predominantly as rhyolitic lava flows and subordinately as trachybasalts and trachyandesites the composition of the numerous dikes varies from basalt to trachyandesite and rhyolite the rhyolites are typified as alkali rhyolites and comendites geochemical criteria characterize a bimodal suite which is not of cogenetic origin the basalts are mantle derived fractionation controlled products whereas the alkali rhyolites and comendites were generated by partial melting of continental crustal rocks the investigated magmatic suite has been compared with equivalent suites from the arabian nubian shield

correlations between the mainshock and the largest aftershock for taiwan earthquakes from the mainshocks of 85 taiwan earthquakes ms 5 and their aftershocks reported in the earthquake data report by neic pde catalogue several correlations between mainshocks and their aftershocks are studied results show that the magnitude difference ms between the mainshock and the largest aftershock slightly increases with the mainshock magnitude ms and varies from 0 1 to 2 2 with two values of 0 3 and 0 9 having the largest numbers of events the mean value of ms is 0 83 0 46 the differences of occurrence time and epicenter between the mainshock and the largest aftershock do not clearly correlate to ms as well as ms for the whole data set 36 5 and 77 7 of the largest aftershocks are located near their individual mainshocks within a distance of 10 and 40 km respectively the difference in occurrence time somewhat increases as the difference of epicenters increases

geochemical and zircon u pb geochronological study of the yangshan a type granite insights into the geological evolution in south anhui eastern jiangnan orogen abstract the early cretaceous yangshan granite is an a type granitic intrusion that was emplaced along the eastern jiangnan orogen in southern anhui province south china the yangshan intrusion mainly consists of syenite porphyry 127 0 0 6 ma and alkali feldspar granite porphyry 126 0 1 0 ma as a part of qingyang jiuhuashan complex intrusion the yangshan a type granites have lower mgo cao co sr and higher rb nb th and hree contents with enrichment in large ion lithophile elements lile and light rare earth elements lree and slightly negative eu anomalies however the syenite porphyry and the alkali feldspar granite porphyry differ in terms of zircon ehf t values small variations in the syenite porphyry from 5 5 to 3 7 corresponding to hf model ages tdmc between 1 42 ga and 1 53 ga and large variations in the alkali feldspar granite porphyry from 6 4 to 4 4 yielding tdmc of 0 90 1 59 ga while both rocks also have similar end t values ranging from 7 02 to 5 47 corresponding nd model ages tdmc are 1 37 1 49 ga falling within the hf model ages we take these features to indicate that the qingyang i type granites which are isotopically similar and yangshan a type granites were originated from partial melting of mesoproterozoic neoproterozoic crust with minor juvenile crust input for the alkali feldspar granite porphyry followed by fractional crystallization in combination with previous studies we propose that the cretaceous a type granitic rocks formed between 135 ma and 122 ma implying an important mesozoic extensional event in eastern jiangnan orogen which facilitated underplating of mantle derived magma and crustal heating this may have occurred in a back arc extension in response to the drift of subduction direction of the paleo pacific plate which started as early as 135 ma ago

late ediacaran 605 580 ma post collisional alkaline magmatism in the arabian nubian shield a case study of serbal ring shaped intrusion southern sinai egypt abstract the serbal pluton is a late neoproterozoic 605 580 ma post collisional a type granites in southern sinai egypt northernmost arabian nubian shield ans it is characterized by discontinuous ring shaped outcrops dislocated by later faulting the pluton intrudes late neoproterozoic metamorphic and high k calc alkaline rocks the serbal pluton mostly comprises an outer zone of alkali feldspar granite surrounding a core of peralkaline granite gradational and sharp contacts in the serbal granites suggest that they were emplaced with a very short time interval still before complete crystallization of the earlier batch serbal granites are highly evolved 75 98 78 52 wt sio2 and display the typical geochemical characteristics of post collisional a type granites namely high sio2 na2o k2o feo mgo ga al zr nb ga and y and low cao mgo ba and sr they are rich in ree and have extreme eu negative anomalies eu eu 0 01 0 23 the chemical characteristics indicate that the peralkaline granite shares many features of granites with the tetrad ree effect the serbal pluton evolved through fractional crystallization of a parental magma derived through partial melting of a juvenile crustal protolith that had been extracted from a source having mantle geochemical and isotopic characteristics the crystallization temperatures using fe ti oxides of the serbal granites point to their formation at high temperatures up to 650 850 c at a shallow depth of emplacement

geochronological geochemical and sr nd hf isotopic studies of the baiyanghe a type granite porphyry in the western junggar implications for its petrogenesis and tectonic setting abstract zircon u pb dates sr nd hf isotopic compositions and major element and trace element geochemistry were determined for the baiyanghe granite porphyry in the western junggar nw china the porphyry has a zircon u pb age of 313 4 2 3 ma is high in sio 2 76 34 78 30 wt and k 2 o na 2 o 8 04 8 85 wt relatively low in mgo 0 01 0 03 wt and cao 0 29 0 39 wt and shows characteristics typical of a type granites because its y nb ratio 0 33 0 51 is lower than 1 2 it can be classified into a 1 group moreover due to its positive values of end t 4 06 5 29 and ehf t 8 18 11 07 and high concentrations of incompatible elements including rb th u and nb the baiyanghe granite porphyry is suggested to have been derived from an oceanic island basalt like mantle source their extremely high initial 87 sr 86 sr ratios 0 7143 0 7469 and high la sm n values 5 13 8 44 could be caused by the involvement of marine sediments the low ba sr and eu concentrations and high values of di 97 3 98 0 of the granite porphyry suggest that its magma had undergone a high degree of fractional crystallization characterized by the features of within plate granites a back arc basin tectonic setting is favored for the petrogenesis of the baiyanghe granite porphyry such a setting indicates that the subduction of the irtysh zaysan oceanic lithosphere beneath the zharma saur arc was still active during the late carboniferous and the collision between the siberia and kazakhstan blocks probably occurred between ca 316 ma and 307 ma

temporal variation of seismic b values beneath northeastern japan island arc 1 analysis of a high quality seismic catalog reveals that the average of seismic b values in the crust beneath most part of northeastern japan island arc decreased from 0 86 between 1984 and 1990 to 0 73 between 1991 and 1995 the two areas with the largest decrease are found to be in the same areas where the coupling between the north american and the pacific plates is the highest as suggested by a recent geodetic study in the same time period the annual seismic moment release increased by 10 times in addition there seems to be a corresponding increase in volcanic activities in the same area one of the most likely interpretations for the observations is an increase in the subduction rate starting from 1991 the timing of this possible increase in subduction rate is consistent with an apparent increase in global seismic activity

petrogenesis of post collisional a type granitoids from the urumieh dokhtar magmatic assemblage southwestern kerman iran constraints on the arabian eurasian continental collision abstract three plutons deh siahan bande bagh and baghe khoshk sharghi collectively referred to as the dbb hereafter in southwestern kerman in the southeastern part of the urumieh dokhtar magmatic assemblage udma of the zagros orogenic belt differ from the typical calc alkaline metaluminous i type intrusions of the region the dbb intrusions have a distinct lithological assemblage varying from diorite through monzogranite and monzonite to alkali feldspar syenite and alkali granite the dbb granitoids are metaluminous to slightly peraluminous alkaline to shoshonitic in composition and have high total alkali contents with k2o na2o high feot mgo values and low cao and mgo contents they are enriched in some liles such as rb and th and hfses such as zr y and rees except eu and depleted in sr and ba relative to primordial mantle and have low concentrations of transitional metals these features along with various geochemical discriminant diagrams suggest that the dbb granitoids are post collisional a type granitoids which had not been recognized previously in the udma the chondrite normalized ree patterns of the dbb granitoids show slightly enriched light rees la sm n 2 26 4 13 negative eu anomalies eu eu n 0 19 0 74 and flat heavy ree patterns gd yb n 0 80 1 87 the negative eu anomaly indicates an important role for plagioclase and or k feldspar during fractional crystallization whole rock rb sr isotope analysis yields an isochron age of 33 1 ma with an initial 87sr 86sr value of 0 7049 0 0001 whole rock sm nd isotope analysis gives endt values from 2 56 to 3 62 at 33 ma the positive endt and low isr values of the dbb granitoids together with their tdm of 0 6 0 7 ga suggest their formation from partial melting of a lithospheric mantle source modified by fluids or melts from earlier subduction processes melting of lithospheric mantle occurred via a dehydration melting process at pressures below the garnet stability field as a consequence of lithospheric mantle delamination or break off of a subducted slab and melting of the lithospheric mantle by upwelling of hot asthenosphere on the basis of rb sr age dating and the post collisional geochemical signatures of the dbb granitoids along with extensive pre collisional volcanic eruptions in middle eocene we suggest late eocene for the time of collision between the arabian and central iranian plates this also implies that the calc alkaline i type intrusions in the southwestern kerman and in other parts of the udma may have formed in a post collisional context

roughness at the base of the seismogenic zone contributing factors the cutout depth of microseismic activity in continental fault zones appears to correspond to the onset of greenschist metamorphic conditions at about 300 c it can generally be modeled as the transition from frictional to quasi plastic behavior in quartzofeldspathic crust shear resistance increases with depth through the frictional regime to peak at the transition beneath which it falls off exponentially with increasing temperature larger earthquake ruptures ml 5 5 nucleate around this transition depth where the highest concentrations of strain energy may accumulate varying depth and amplitude of the peak shear resistance along strike induce fluctuations in strain energy concentration at the base of the seismogenic zone factors affecting the depth of the transition include crustal composition geometry and mode of faulting fluid pressure levels in the frictional regime and water content in the quasi plastic regime quasi plastic strain rate and geothermal gradient evaluation of their relative importance is complicated because several are interdependent however compositional change may cause abrupt irregularities in seismogenic depth and peak shear resistance while regional variations in heat flow look to be particularly effective in creating long wavelength heterogeneities in strain energy concentration affecting faulting style

petrogenesis and tectonic implications of late carboniferous a type granites and gabbronorites in nw iran geochronological and geochemical constraints abstract carboniferous igneous rocks constitute volumetrically minor components of iranian crust but preserve important information about the magmatic and tectonic history of sw asia ghushchi granites and gabbronorites in nw iran comprise a bimodal magmatic suite that intruded ediacaran cambrian gneiss and are good representatives of carboniferous igneous activity precise sims u pb zircon ages indicate that the gabbronorites and granites were emplaced synchronously at 320 ma ghushchi granites show a type magmatic affinities with typical enrichments in alkalis ga zr nb and y depletion in sr and p and fractionated ree patterns showing strong negative eu anomalies the gabbronorites are enriched in lrees nb ta and other incompatible trace elements and are similar in geochemistry to oib type rocks granites and gabbronorites have similar e nd t 1 3 to 3 4 and 0 1 to 4 4 respectively and zircon e hf t 1 7 to 6 2 and 0 94 to 6 5 respectively the similar variation in bulk rock e nd t and zircon e hf t values and radiometric ages for the granites and gabbronorites indicate a genetic relationship between mafic and felsic magmas either a crystal fractionation or silicate liquid immiscibility process further work is needed to resolve petrogenetic details the compositional characteristics of the bimodal ghushchi complex are most consistent with magmatic activity in an extensional tectonic environment this extension may have occurred during rifting of cadomian fragments away from northern gondwana during early phases of neotethys opening

seismicity in the hellenic volcanic arc relation between seismic parameters and the geophysical fields in the region summary a study of the spatial distribution of seismicity and seismic hazard and geophysical parameters is undertaken along the hellenic volcanic arc hva seismicity of the area is divided in a cellular manner allowing analysis of the localized seismicity parameters and representation of their regional variation as contour maps extreme value analysis locates a zone of highest seismicity just west of centre of the hva around the cyclades islands non probabilistic modelling of the strain energy release process in terms of magnitudes equivalent to the average annual energy release rate m and the maximum possible energy release in a seismic cycle m3 enhances this picture maximum values of m and m3 are more tightly localized in the central cyclades west of amorgos island and also in the east of the hva in the sporadhes north west of rhodes isocyclic contours of the waiting times for m3 show values in excess of 70 years in the cyclades and eastern sporadhes i e the zones of largest earthquakes show the longest strain accumulation periods the waiting time for the hva as a whole is about 54 years and at present it appears to be about 75 per cent through to accumulation of the notional maximum strain energy the b value of the magnitude frequency distribution shows a consistent spatial variation along the hva which is not sensitive to subdivision into different focal depth ranges regional contour maps of the b values and maps of local values of heat flow magnetic and electrical anomalies compared with the bouguer gravity anomaly map indicate correlations which reflect the deformation of the aegean shallow crust in relation to the deep intrusive magmatic processes the correlations between the different geophysical fields are displaced commensurate with an aegean extension of approximately 45 km

b values of shallow earthquakes in taiwan abstract in taiwan the b values of earthquakes with focal depths of less than 35 km are smaller offshore than on land on land except for the coastal range the b value correlates to the degree of metamorphism of rocks which decreases inland from east to west small b values appear at the leading edge of the subducting slab of the philippine sea plate that plunges underneath northern taiwan possibly indicating high stress due to a bending of the slab large b values in an area including the volcano groups in northern taiwan may be due to the remnant geothermal effect after past volcanic activities besides small b values on land are mainly associated with low bouguer gravity anomalies offshore small b values are related to high bouguer gravity anomalies particularly in regions with a large gravity gradient

geochronological and geochemical constraints on the petrogenesis of the early paleoproterozoic potassic granite in the lushan area southern margin of the north china craton abstract we conducted a geochronological and geochemical study on the paleoproterozoic potassic granites in the lushan area southern margin of the north china craton ncc to understand the tectonic regime of the ncc at 2 2 2 1 ga this rock suite formed at 2194 29 ma the rocks are rich in sio2 76 10 77 73 wt and k2o 5 94 6 90 wt with high k2o na2o contents from 7 56 wt to 8 48 wt but poor in cao 0 10 0 28 wt p2o5 0 02 0 05 wt and mgo 0 01 0 30 wt mg 1 08 27 3 indicating they experienced fractional crystallization major element compositions suggest the potassic granites share an affinity with high k calc alkaline granite even though the lushan potassic granitic rocks have high a cnk ratios 1 11 1 25 which can reach peraluminous feature the very low p2o5 contents and negative correlation of p2o5 and sio2 ruling out they are s type granites different from peralkaline a type granites the lushan potassic granites have variable zr concentrations 160 344 ppm 226 ppm on average and 10 000 ga al ratios 1 76 3 00 together with high zircon saturation temperatures tzr 826 885 c indicating they are fractionated aluminous a type granites enriched lree la yb n 9 72 81 8 negative eu anomalies and low sr y with no correlations in sr y and sr zr versus cao suggest the possible presence of ca rich plagioclase and absence of garnet in the residual magmatic zircon grains have variable ehf t values 2 4 to 7 3 with zircon two stage hf model ages tdmc varying from 2848 ma to 2306 ma mostly around ca 2 5 ga and are plotted in the evolution line of crustal felsic rock we propose that the rocks mainly formed by partial melting of ca 2 50 ga tonalitic granodioritic crust as a result of upwelling mantle derived magmas which provided thermal flux and source materials in an intra continent rifting the ca 2 2 ga magmatism suggests that intra continental rifting occurred at 2 35 1 97 ga at least in the southern margin of the ncc after its final cratonization in the late neoarchean

granulite xenoliths from western saudi arabia the lower crust of the late precambrian arbian nubian shield mafic and intermediate granulite xenoliths collected from cenozoic alkali basalts provide samples of the lower crust in western saudi arabia the xenoliths are metaigneous two pyroxene and garnet granulites mineral and whole rock compositions are inconsistent with origin from red sea rift related basalts and are compatible with origin from island arc calc alkaline and low potassium tholeiitic basalts most of the samples are either cumulates from mafic magmas or are restites remaining after partial melting of intermediate rocks and extraction of a felsic liquid initial87sr 86sr ratios are less than 0 7032 except for two samples at 0 7049 the sm nd data yield tdm model ages of 0 64 to 1 02 ga similar to typical arabian nubian shield upper continental crust the isotopic data indicate that the granulites formed from mantle derived magmas with little or no contamination by older continent crust calculated temperatures and pressures of last reequilibration of the xenoliths show that they are derived from the lower crust calculated depths of origin and calculated seismic velocities for the xenoliths are in excellent agreement with the crustal structure model of gettings et al 1986 based on geophysical data from western saudi arabia estimation of mean lower crustal composition using the granulite xenoliths and the gettings et al 1986 crustal model suggests a remarkably homogeneous mafic lower crust and an andesite or basaltic andesite bulk composition for pan african juvenile continental crust

crystal fractionation and the evolution of intra plate hy normative igneous suites insights from their feldspars feldspars and normative feldspar constituents of bulk magma show complexes and anorogenic granites is associated with hotspot and continental rift environments a major chartrends supportive of fractional crystallization in the three main types of hy normative intraplate suites that contain qz oversaturated acteristic of this magmatism is the production of suites of compositionally diverse rocks that are temporally and rocks ocean island and continental alkalic suites ocean island tholeiitic suites and continental tholeiitic suites these suites are spatially associated much is still unknown about the processes that have led to the diversity of magmas within characterized by the presence of a single feldspar in each suite member a shift of this feldspar from plagioclase to alkali feldspar such suites or to the global diversity of intra plate suite types and k enrichment of alkali feldspar with decreasing temperature in the trachytic members the modal feldspars provide evidence for a many ocean island and continental hotspot and continental rift related suites are characterized by rocks with reaction relationship between feldspars and indicate a build up of magmatic volatile content towards saturation with progressive high alkali silica ratios that fall into the alkalic field of irvine baragar 1971 fig 1 regardless of their state fractionation of a parental magma having low initial volatile content the feldspar and normative feldspar evolutionary paths are unique of silica saturation such alkalic suites range from those that are strongly silica undersaturated containing rocks for each of the three suite types but similar for different suites within the same type this characteristic extends to the felsic members such as nephelinites or leucitites in the more potassic making it easy to distinguish between rhyolitic or granitic rocks suites to mildly silica undersaturated suites the kenfrom the different suite types the feldspars in natural volcanic nedy series of miyashiro 1978 containing alkali basalts suites commonly show evidence for a polybaric history particularly silica undersaturated trachytes and phonolites and in the least evolved suite members late stage feldspars of the finally to hy normative suites the coombs trend of intermediate members and feldspars of the most evolved members miyashiro 1978 that include olivine basalts trachytes show paths indicative of significantly lower temperature and pressure and rhyolites hy normative alkalic suites that contain regimes silica oversaturated rocks on ocean islands are widespread and include those from ascension island e g harris 1983 the samoan islands macdonald 1968 terceira azores e g white et al 1979 and clarion island mexico

the seismic b value and its correlation with bouguer gravity anomaly over the shillong plateau area tectonic implications abstract clues to the understanding of intra and inter plate variations in strength or stress state of the crust can be achieved through different lines of evidence and their mutual relationships among these parameters bouguer gravity anomalies and seismic b values have been widely accepted over several decades for evaluating the crustal character and stress regime the present study attempts a multivariate analysis for the shillong plateau using the bouguer gravity anomaly and the earthquake database and establishes a causal relationship between these parameters four seismic zones zones i iv with widely varying b values are delineated and an excellent correlation between the seismic b value and the bouguer gravity anomaly has been established for the plateau low b values characterize the southwestern part zone iv and a zone zone iii of intermediate b values separates the eastern and western parts of the plateau zones i and ii which have high b values positive bouguer anomaly values as high as 40 mgal a steep gradient in the bouguer anomaly map and low b values in the southwestern part of the plateau are interpreted as indicating a thinner crustal root uplifted moho and higher concentration of stress in comparison the negative bouguer anomaly values flat regional gradient in the bouguer anomaly map and intermediate to high b values in the northern part of the plateau are consistent with a comparatively thicker crustal root and lower concentration of stress with intermittent dissipation of energy through earthquake shocks further depth wise variation in the b value for different seismic zones delineated under this study allowed an appreciation of intra plateau variation in crustal thickness from 30 km in its southern part to 38 km in the northern part the high b values associated with the depth coinciding with lower crust indicate that the shillong plateau is supported by a strong lithosphere

relationships between crustal contamination and crystallisation in continental flood basalt magmas with special reference to the deccan traps of the western ghats india the upper part of the deccan traps sequence bushe to mahabaleshwar formations shows a statistically significant tendency for the most mafic lavas to be the most contaminated by crustal materials this is the reverse of the relationship shown by suites evolving by contamination accompanied by fractional crystallisation afc the observed correlations e g between mg number and sr isotope initial ratios are partly an accidental consequence of the fact that the most mafic lavas are more abundant in the lower part of the sequence while contaminant availability declines in the upper part it is probable however that the correlations are augmented by increased contamination of hotter magma batches during ascent through dykes a process during which fractional crystallisation is suppressed by magmatic turbulence the absence of afc relationships suggests that most of the contamination took place during the ascent stage rather than in a magma chamber other continental flood basalt provinces such as the parana and etendeka do show afc relationships and it is speculated that this may be a result of magma chamber contamination coupled with flow rates which prevent contamination during ascent

geochronology mineralogy and geochemistry of alkali feldspar granite and albite granite association from the changyi area of jiao liao ji belt implications for paleoproterozoic rifting of eastern north china craton abstract paleoproterozoic granites divided into alkali feldspar granite and albite granite were newly discovered in the changyi area of the jiao liao ji belt from the eastern block of the north china craton la icp ms zircon u pb dating shows that the alkali feldspar granite was emplaced at 2193 ma whereas the albite granite intruded at 2171 ma these granites have high sio2 na2o k2o zr nb ga y and hree contents and show remarkably low cao eu ba and sr concentrations strongly suggesting their a type affinities zircon saturation thermometry and alt in biotite geobarometer indicate that the alkali feldspar granite crystallized at temperatures of 823 856 c averaging at 839 c and pressures of 1 54 2 73 kbar averaging at 2 05 kbar while the albite granite was cooled at the temperatures of 851 853 c and the pressures of 2 34 2 64 kbar averaging at 2 45 kbar combined with such high temperatures and low pressures the crustal like nd hf isotopic compositions nd t 5 3 to 4 4 hf t 7 0 to 3 8 support their derivation from the shallow melting of archean crustal rocks under high heat flow however the contrasted k2o and na2o compositions between the alkali feldspar granite k2o 4 76 5 14 wt na2o 4 76 5 14 wt and the albite granite k2o 0 29 0 44 wt na2o 6 15 6 56 wt imply that they may have been derived from distinct source rocks or have undergone different magmatic processes genetic modeling suggests that the alkali feldspar granite was originated from melting of granodioritic rocks the albite granite however was most likely derived from the reworking of plagioclase rich layers after the extraction of a type melts coupled with other studies on sedimentary and volcanic successions in the jiao liao ji belt the unusual association of the a type alkali feldspar granite and albite granite indicates that the southern segment of the jiao liao ji belt experienced continental rifting during 2 1 2 2 ga

mapping of b value beneath the shillong plateau abstract the seismic parameter b has been computed over rectangular grid of dimension 0 3 0 8 at four depths range 0 13 km first layer 13 1 26 km second layer 26 1 39 km third layer and 39 1 52 km fourth layer beneath the shillong plateau area the four depths were carefully selected based on the crustal structure and distribution of hypocentres the dimension of each grid was chosen so as to have enough events that can represent the b value at the respective layer finally two dimensional mapping was done at these depth levels considering the respective b value over each grid this analysis includes viz low b value all through the first layer and a trend of increasing b value which was initially towards north changes to northwest eastern and western parts of the second and third layers document almost moderate b values whereas the north south oriented central part of layer second is apparently dominated by low b values which seems to divide the area broadly into three parallel zones based on b values in the deeper part fourth layer beneath the shillong plateau a moderate b value that was initially trending towards north becomes high near the northeastern part this phenomenon may be associated with higher heterogeneity of the medium and interestingly this region lies between the lower crust and upper mantle possibly documents lower degree of seismic coupling where the shillong plateau is being supported by the strong indian lithosphere at these depths in addition minima were noted towards the southern parts of layers first second and third which may presumably be related with steeply bouguer gravity anomaly it is thus less clear that the occurrence of earthquakes beneath the shillong plateau whether is attributed to faults or lineaments at intermediate to deeper level however a correlation between high b values in few parts of each layer and deep seated minor faults cannot be ruled out

petrogenesis of u and mo bearing a2 type granite of the gattar batholith in the arabian nubian shield northeastern desert egypt evidence for the favorability of host rocks for the origin of associated ore deposits abstract hydrothermal ore deposits associated with granitic rocks are the result of combinations and series of successive processes events and conditions in a magma system and at post magmatic stage the metal content of a granitic magma as well as fractional crystallization metal ligand complexation emplacement mechanisms and tectonic processes influence the metal precipitation and content of a hydrothermal ore deposit the present study of the gattar batholith evaluates how these processes contribute to the generation of an ore deposit gattar batholith in the north eastern desert of egypt as part of the northern region of the arabian nubian shield ans is geographically mineralogically and geochemically divided into two distinctive areas the southern part mainly consists of syenogranite while the northern part is dominated by highly evolved alkali feldspar granite uranium and mo mineralization occurring here is mostly limited to the margin of the highly evolved alkali feldspar granites new u pb zircon geochronology within this study indicates an age of 620 600 ma although high common pb and discordant age data of many zircon grains reflect alteration by f rich fluids some zircons with distinct older u pb ages were considered to be inherited from the wall rocks representing juvenile crust of the ans the two different granitic rocks are comagmatic in origin and have a type characteristics generated by partial melting of lower juvenile crust of the ans geochemical data are in good agreement with a magmatic origin of the alkali feldspar granites suggesting fractional crystallization of a syenogranitic source as the most favorable process of their formation petrography geochemistry and geochronology studies of the gattar granites along with field observations provide evidence for multiple intrusions as a result of successive magma pulses with different chemical composition this led to the formation of reverse zoning within the intrusive complex this kind of magma emplacement promotes the escape of exsolved metal bearing volatile rich fluids into the boundary of the hammamat sedimentary rocks hsr and gattar granite at the northern part of the batholith build up of volatiles is a common phenomenon in granitic rocks and typically results in enhanced contents of f alkalis and ore metals released at subsolidus stage

latest cretaceous a 2 type granites in the sakarya zone ne turkey partial melting of mafic lower crust in response to roll back of neo tethyan oceanic lithosphere abstract an integrated study of comprehensive geochronological geochemical and sr nd hf isotopic data was undertaken for the a type topcam pluton that intruded within the sakarya zone ne turkey with the aims of elucidating its origin and tectonic significance and gaining new insights into the generation of aluminous a type granites new la icp ms zircon u pb crystallization ages of 72 and 73 ma indicate emplacement in the late cretaceous time just after extensive metaluminous i type magmatism in the area the pluton consists mainly of alkali feldspar quartz plagioclase amphibole and biotite with accessory minerals such as magnetite apatite and zircon the outcrop is composed of granite syenite monzonite and quartz monzonite and possesses a wide range of sio2 content 57 70 wt with elevated ga al ratios and low mg mostly

a tectonic transition from closure of the paleo asian οcean to subduction of the paleo pacific plate insights from early mesozoic igneous rocks in eastern jilin province ne china abstract the timing of tectonic transition from the paleo asian oceanic regime to the paleo pacific regime in the easternmost central asian orogenic belt remains controversial to constrain the event we present new zircon u pb ages hf isotopic compositions and whole rock major and trace element data for early mesozoic igneous rocks from eastern jilin province ne china these new ages together with existing age data indicate that early mesozoic magmatism in the kaiyuan yanji area can be subdivided into four stages early triassic ca 250 ma early middle triassic 249 235 ma late triassic 229 208 ma and latest triassic to early jurassic 207 175 ma the early triassic igneous rocks constitute a bimodal igneous rock association that formed in an extensional environment caused by break off of the subducting slab during final closure of the paleo asian ocean the early middle triassic magmatism is dominated by adakitic granitoids whose primary magmas were derived from partial melting of thickened mafic lower crust suggesting that the north china craton and songliao xilinhot block were still undergoing collisional orogenesis at 249 235 ma the late triassic igneous rocks comprise a typical bimodal association of rocks in an e w trending belt formed in a post orogenic extensional environment related to final closure of the paleo asian ocean the latest triassic to early jurassic igneous rocks have calc alkaline characteristics were emplaced as a ne sw trending belt parallel to the eastern margin of eurasia and formed in an active continental margin setting associated with initial subduction of the paleo pacific plate we conclude that the tectonic transition between the paleo asian and the paleo pacific regimes took place during the latest triassic

tuffaceous deposition in the newcastle coal measures challenging existing concepts of peat formation in the sydney basin new south wales australia abstract the late permian newcastle coal measures of the northern sydney basin australia contain numerous volcanic ash deposits occurring as both interseam tuffs and intraseam tonsteins these tuffaceous units have been used to correlate seams of the newcastle coal measures with the stratigraphically equivalent wollombi coal measures in the adjacent hunter coalfield such correlations across the width of the northern sydney basin are based not on only tuffaceous markers but also on chemical and maceral profiles within individual coal plies and carbonaceous shales these correlations imply a lateral continuity of the peat forming environment previously unrecognised in the sydney basin and have led directly to the discovery of a new open cut coal resource in the hunter coalfield the uniform distribution of tonsteins and coal plies also challenges many existing concepts of peat formation it is proposed that the peat surface was predominantly below the water table and the term lowered mire is proposed to describe this environment a subaqueous peat surface would protect thin volcanic ash deposits from subsequent redistribution by rainfall and surface runoff and is consistent with a lack of tree preservation within the intraseam tonsteins it is envisaged that trees were generally restricted to the peat margins and to specific horizons where the peat surface was exposed by a fall in the water table long distance correlations of tonsteins also contradict models of coal formation incorporating lateral peat migration where time constant horizons such as tonsteins should transgress the coal seam profile over large distances

late paleozoic post collisional magmatism in the eastern tianshan belt northwest china new insights from geochemistry geochronology and petrology of bimodal volcanic rocks abstract the late carboniferous to permian marks an important phase of terrane amalgamation through accretion collision in the central asian orogenic belt caob the tianshan belt forms part of this sequence where the post collisional event generated an e w trending bimodal volcanic zone that extends for ca 500 km from the southern bogda mt to the easternmost tianshan belt here we report the petrology geochemistry and geochronology of the bimodal volcanic rocks to characterize the post collisional tectonic evolution in late paleozoic the major element chemistry of the basalt and rhyolite samples indicates a bimodal high k calc alkaline affinity the basalts are characterized by high abundance in tio2 th u and pb and depletion in nb ta and p together with slight enrichment in lree contents and low hfse lree ratios the rhyolites show a close affinity to aluminous a type granites with enrichment in k na zr ce y and depletion in p nb ta and ti they also exhibit fractionated ree patterns with prominent negative eu anomalies the petrographic and geochemical data suggest that this bimodal rock series was generated in a post collisional setting the mafic rocks are likely derived from a metasomatized lithospheric mantle assimilation of different crustal components played a minor role in the genesis of these basaltic rocks the la icp ms analysis on zircons from four rhyolites and two basalts yielded similar ages ranging from 295 8 2 8 to 293 3 1 7 ma suggesting an early permian event zircons from the basalts show a wide ehf t range from 0 49 to 13 whereas those from the rhyolites show two groups of ehf t values from 5 to 3 and from 6 to 12 suggesting a mixing of crust mantle material the magmatic zircons from the bimodal volcanic rocks yielded two peaks of tdm2 between 600 820 ma and 1160 1360 ma probably representing two significant episodes of continental crust growth the bimodal volcanic rocks are correlated with the early stage of post collision our results suggest that vertical crustal growth through mantle derived magmas in post collisional setting also played a major role in the construction of the caob

age petrogenesis and tectonic implications of early devonian bimodal volcanic rocks in the south altyn nw china abstract in this paper we report zircon u pb dating hf isotopes geochemical and sr nd isotopic data with the aim the petrogenesis and regional tectonic evolution of early devonian bimodal volcanic rock in the south altyn nw china new la icpms zircon u pb isotopic data constrained them at ca 406 ma the mafic samples are characterized by high fe cr and ni contents low ti and mg contents slightly enriched lree patterns and low la yb n la nb and la ta ratios and positive e nd t values 3 3 to 3 4 indicating that they were likely derived from strong batch melting of the asthenosphere in the spinel facies field the felsic rocks show an a type affinity with high alkalis fe ga zr nb ce and y contents low mg sr content high rb sr and ga al ratios enrichment in lile e g rb k th u and lree and depletion in ba sr nb ta p and ti and fractionated ree patterns with very strong negative eu anomalies these features along with distinct e nd t values 0 5 to 2 3 and mostly positive e hf t 0 29 to 5 18 indicate that the felsic rocks were mainly generated by partial melting of the crust in low pressure and high temperature conditions and simultaneously underwent slight magma mixing of such melts with mantle magma according to the petrogenetic schemes and geological background of the early devonian bimodal volcanic rocks tholeiite and a type dacite rhyolite they should have formed in a post collisional extensional setting moreover on the basis of spatial and temporal distribution and formation mechanism the tectonic magmatic evolution of the early paleozoic south altyn tagh could be divided into three stages 505 472 ma continental collision the magmatite formed under high pressure conditions due to the deep subduction and initial tearing of continental slab 467 450 ma continental slab break off the magmatite formed at high temperature and low pressure in virtue of felsic upper crust uplifting and mantle magma underplating and 432 385 ma post collisional extension the magmatite consists of a type granites and bimodal volcanic rocks which are the products of the interaction between mantle and crust and asthenosphere upwelling

synchronous a type and adakitic granitic magmatism at ca 2 2 ga in the jiao liao ji belt north china craton implications for rifting triggered by lithospheric delamination abstract the jiao liao ji belt jljb underwent back arc or intra continental rifting during the early palaeoproterozoic but the underlying mechanism remains unclear to address this issue this study focuses on the petrogenesis of widespread palaeoproterozoic granitoids on liaodong peninsula china zircon u pb dating and geochemical and hf isotopic data suggest that these granitoids were formed at ca 2 2 ga and they can be divided into a type and adakitic granites the a type granites have relatively high sio2 k2o zr ga nb and y contents and low cao mgo al2o3 and sr contents based on these characteristics ehf t values 0 8 to 2 8 and tdm2 ages 2797 2569 ma the a type granites are inferred to be derived from neoarchaean tonalite trondhjemite granodiorites in a rift setting in contrast the coeval adakitic granites have relatively high na2o al2o3 and sr contents and high sr y and lan ybn ratios but low mgo ni yb and y contents suggesting a magma source with garnet but no plagioclase in the residue beneath thickened lower crust their variable ehf t values 8 5 to 6 9 and tdm2 ages 3276 2305 ma indicate that the adakitic magmas were mainly generated by the partial melting of meso neoarchaean crust the co existence of contemporaneous ca 2 2 ga adakitic and a type granites provides evidence that the jljb underwent regional rifting in the palaeoproterozoic most likely due to delamination of a thickened lithosphere as follows 1 in the neoarchaean the lower crust of the longgang block underwent granulite and or eclogite facies metamorphism due to continuous thickening which resulted in increasing lower crustal density 2 the thickened lower crust became unstable and delaminated at ca 2 2 ga asthenospheric upwelling following this lithospheric delamination triggered the thinning of the overlying lithosphere the upper crust and remnant thickened lower crust were partially melted to form the a type and adakitic granites respectively the rifting likely resulted in the separation of the longgang and nangrim blocks prior to their amalgamation in the late palaeoproterozoic to form the jljb