structure emplacement and tectonic setting of late devonian granitoid plutons in the tepla barrandian unit bohemian massif the st novice and cista granodiorite tonalite plutons are small 27 and 38 km2 respectively intrusions that are largely discordant to regional ductile structures in the center of the upper crustal tepla barrandian unit bohemian massif their whole rock and trace element compositions are consistent with medium k calc alkaline magma generated above a subducted slab in a continental margin arc setting the u pb zircon age of the st novice pluton newly determined at 375 2 ma using the laser ablation icp ms technique is within the error of the previously published pb pb age of 373 1 ma for the cista pluton the two plutons also share other characteristics that are typical of concentrically expanded plutons ceps such as elliptical cross section in plan view steep contacts inferred downward narrowing conical shape faint normal zoning and margin parallel magmatic foliation decoupled from the regional host rock structures we interpret the st novice and cista plutons as representing the initial late devonian stage of much more voluminous early carboniferous arc related plutonism represented most typically by the central bohemian plutonic complex in the upper crust of the central bohemian massif these two plutons are important tectonic elements in that they indicate an overall shift of the arc related plutonic activity from the nw to the se accompanied with a general compositional trend of the magmas from medium k calc alkaline to shoshonitic ultrapotassic such a pattern is compatible with se directed subduction of the saxothuringian ocean beneath the tepla barrandian overriding plate as a cause of arc related magmatism in this part of the bohemian massif

the tectonic evolution of the irtysh tectonic belt new zircon u pb ages of arc related and collisional granitoids in the kalaxiangar tectonic belt nw china abstract precise geochronological constraints of the irtysh tectonic belt situated between the saur island arc and the altay terrane are crucial to a better understanding of the tectonic evolution of the central asian orogenic belt caob recently we discovered repeatedly deformed arc related and collisional granitoids in the kalaxiangar tectonic belt ktb which is located in the eastern part of the irtysh tectonic belt in this study we report new whole rock geochemical zircon u pb and hf isotopic data of the arc related and collisional granitoids our data reveal that 1 arc related granodioritic porphyries formed at ca 382 374 ma recrystallized zircon grains from a ultra mylonitic granodiorite of the laoshankou zone in the southern ktb display a u pb age of ca 360 ma 2 syn collisional granodioritic porphyries which distribute along faults and parallel to the cleavage were emplaced at ca 367 356 ma with e hf t values varying from 7 8 to 14 2 and hf model ages from 873 to 459 ma 3 a post collisional a type granodioritic porphyry which crosscuts the nw nnw trending schistosity of the metasedimentary country rocks at a low angle has an age of ca 324 320 ma while the e hf t values range from 7 6 to 14 4 with hf model ages from 850 to 416 ma 4 post collisional strike slip a type granite dykes exposed along strike slip faults gave ages between 287 and 279 ma whereas the e hf t values range from 4 9 to 12 7 and the hf model ages from 995 to 500 ma and 5 a type biotite granite dykes which intruded along conjugate tension joints have ages of 274 271 ma and e hf t values from 1 5 to 13 2 with hf model ages from 1196 to 454 ma consequently we propose that the collision between the saur island arc and the altay terrane occurred in the early carboniferous ca 367 356 ma and the subsequent post collisional tectonic process continued to the late carboniferous ca 324 320 ma it is further suggested that the irtysh tectonic belt underwent large scale strike slip deformation during the mid permian between 287 and 279 ma the termination of the irtysh tectonic belt orogeny is thought to have also occurred during the mid permian between 274 and 271 ma

petrogenesis and geodynamic implications of neoproterozoic gabbro diorites adakitic granites and a type granites in the southwestern margin of the yangtze block south china abstract the occurrence of a type granites following adakitic granites can provide unique insights into the tectonic evolution of subduction zone this paper presents a comprehensive study of zircon u pb hf isotopes and whole rock geochemistry on the neoproterozoic gabbro diorites biotite granites and k feldspar granites in the southwestern margin of the yangtze block south china zircon u pb dating of three distinctive intrusions yield concordant ages of 810 4 2 0 ma for gabbro diorites 800 3 2 1 ma for biotite granites and 749 1 2 0 ma for k feldspar granites the gabbro diorites are sodic and calc alkaline rocks with low sio2 52 62 53 87 wt medium mgo 2 67 3 41 wt high fe2o3t 7 18 7 49 wt and cao 5 68 7 50 wt contents they display high th zr and rb y ratios but low nb zr and nb y ratios together with their positive whole rock end t 1 0 to 1 5 and zircon ehf t values 3 66 to 8 18 we suggest that these gabbro diorites were derived from the partial melting of depleted lithospheric mantle modified by subduction related fluids the biotite granites display relatively high sr contents 335 395 ppm sr y ratios 38 9 54 3 low y 7 04 9 71 ppm and yb contents 0 78 1 08 ppm resembling the adakitic granites their low mg 36 41 values cr 2 94 3 59 ppm and ni 1 32 1 55 ppm contents as well as positive end t 0 5 to 0 6 and ehf t values 1 62 to 8 07 indicate that they were formed by partial melting of thickened juvenile mafic lower crust probably within the existence of garnet the k feldspar granites have high sio2 76 61 77 14 wt and alkalis na2o k2o 8 55 9 69 wt contents high 10 000 ga al 2 56 2 80 ratios and differentiation index 95 3 96 9 indicating the affinity to highly fractionated a type granites we suggest that these a type granites were mainly generated by the partial melting of felsic crustal rocks under low pressure condition and subsequently extensive fractional crystallization is significant taking into account previous studies from the western yangtze block south china we propose that the gabbro diorites adakitic granites and a type granites in this study were formed in persistent subduction process during the neoproterozoic

genesis of high potassium calc alkaline peraluminous i type granite new insights from the gaoligong belt granites in southeastern tibet plateau abstract silicic magmas primarily felsic i and s type granite sensu lato play a key role in understanding the compositional evolution and differentiation of the continental crust however the genetic models of felsic i type granites remain controversial herein we investigate the gaoligong granite sensu lato belt in southern tibet and compare its features with an extensive dataset that we compiled on high potassium calc alkaline peraluminous i type granite from typical granitic belts around the word with a view to gain insights on the genesis of felsic i type granites the early cretaceous granites from gaoligong belt mostly belong to high k calc alkaline peraluminous i type series zircon lu hf ehf t 16 3 0 9 and whole rock sr nd isotopic data end t 14 6 3 0 on these rocks show highly variable and evolved nature suggesting that the granites were generated by partial melting of lower crustal materials with possible involvement of upper crustal materials followed by mixing leading to marked variation in source compositions compilation of the dataset and comparison with felsic i and s type granites show the following salient features 1 possibly distinct trends of al2o3 p2o5 k2o rb sr pb th u and ga vs mgo feot between the felsic i type granites and those s types and 2 there are notably higher and variable zircon hf ehf t 10e units and whole rock sr nd end t 5e units isotopic compositions of i type granites than those of the s types comparison with experimental liquids and other typical cases around the world indicate that the felsic i type granites from gaoligong are similar to those secondary i type granites where mixing processes and extensive partial melting of the heterogeneous lower crust by a mantle like magma control the variable components the range of compositional diversity is significantly higher for the studied felsic i type granites than those typical s type granites from north queensland our study provides further insights into the application of geochemical and isotopic proxies to differentiate felsic i and s type granites

origin of high potassium talc alkaline i type granitoids many i type granitoid magmas are generated through partial melting of older metaigneous rocks and the compositions of such melts are broadly calc alkaline and metaluminous these melts are granitic to tonalitic and result from thermal extremes in their lower crustal source regions data on the experimental partial melting of common crustal rocks suggest that high k i type granitoid magmas can be derived only from the partial melting of hydrous calc alkaline to high k calc alkaline mafic to intermediate metamorphic rocks in the crust because of their low k2o contents metabasaltic rocks of all kinds are unsuitable as sources and models that propose mixing of mantle derived basaltic magmas and crustal melts are also inadequate there is no requirement that i type calc alkaline magmatism be related in any way to subduction processes

granitic magmas with i type affinities from mainly metasedimentary sources the harcourt batholith of southeastern australia the high k calcalkaline granitic rocks of the 370 ma post orogenic harcourt batholith in southeastern australia have i type affinities but are mildly peraluminous and have remarkably radiogenic isotope characteristics with 87sr 86srt in the range 0 70807 to 0 714121 and endt in the range 5 6 to 4 3 this batholith appears to be a good example of magmas that were derived through partial melting of distinctly heterogeneous source rocks that vary from intermediate meta igneous to mildly aluminous metasedimentary rocks with the balance between the two rock types on the metasedimentary side such transitional s i type magmas formed from mainly metasedimentary source rocks may be more common than is generally realised the harcourt batholith also contains mainly granodioritic igneous microgranular enclaves imes like their host rocks the imes are peraluminous and have rather radiogenic isotope signatures 87sr 86srt of 0 71257 0 71435 and endt of 7 3 to 4 3 though some are hornblende bearing origins of these imes by mixing a putative mantle end member with the host granitic magma can be excluded because of the variability in whole rock isotope ratios and for the same reason the ime magmas cannot represent quench cumulates autoliths from the host magmas less abundant monzonitic to monzosyenitic imes cannot represent accumulations of magmatic biotite and or alkali feldspar because k feldspar is absent and there is no co enrichment of k2o and feo mgo nor can they be mixtures of anything plausible with the host rock magma the granodioritic imes probably originated through high degrees of assimilation of a range of crustal materials partial melts by basaltic magmas in the deep crust and the monzonitic imes as melts of enriched subcontinental mantle such enclave suites provide little or no information on the chemical evolution of their host granitic rocks

genesis of the high sr y rocks in qinling orogenic belt central china abstract the genesis of high sr y rocks and their connection with specific geodynamic settings are not yet resolved triassic granitic intrusions with high sr y ratios are widespread in the qinling orogenic belt of china three intrusions of granodiorite granite porphyry and dacite porphyry in the western qinling orogenic belt have zircon la icp ms u pb ages of 237 216 ma the rocks are metaluminous to weakly peraluminous and are characterized by enrichment in large ion lithophile elements e g rb ba th and u depletion in high field strength elements e g nb ta and ti high sr y 31 8 77 5 and la yb n 13 6 72 6 ratios very low y 5 3 16 3 ppm and yb 0 35 1 53 ppm contents and negligible eu anomalies their 87sr 86sr i ratios 0 70715 0 70884 end t 5 93 to 3 07 zircon ehf t 2 34 to 0 85 values and ancient two stage model ages tdm2nd 1 26 1 47 ga tdm2hf 1 20 1 39 ga and characteristic of low temperature granitoid indicate that they are partial melts of neoproterozoic lower crust with input of enriched mantle derived mafic magma there is no evidence of formation through high pressure magmatic processes and a proposed partial melting model indicates that the high sr y signature of these intrusive rocks may have been inherited from source rocks lower crustal rocks of the south qinling terrane studies of regional tectonic evolution have shown that the rocks were formed in a subduction regime and or a subduction to initial collision transitional setting a high sr y ratio in the magma source may therefore have imparted the high sr y signature rather than it being associated with a specific geodynamic setting

hydrogen and oxygen isotope geochemistry of a type granites in the continental margins of eastern china hydrogen and oxygen isotope studies of both whole rock and mineral separates were carried out for five representative atype granites in eastern china from north to south the whole rock d d and d 18 o values vary from 2145 to 282 and from 21 2 to 5 0 for nianzishan pluton from 2135 to 2110 and from 1 6 to 6 7 for shanhaiguan pluton and from 2145 to 2111 and from 1 5 to 9 1 for laoshan massif respectively the highest whole rock dd and d 18 o values are observed in suzhou pluton and range from 281 to 259 and from 3 5 to 9 2 respectively homogeneous d d and d 18 o values are found in kuiqi massif ranging from 2113 to 299 and from 5 6 to 8 5 respectively the results show that the large variabilities in the hydrogen and oxygen isotope ratios are mainly related to the diverse processes of magma evolution such as magma degassing fractional crystallization as well as post magmatic alteration by local meteoric water under subsolidus conditions the initial d d and d 18 o values of the a type granites in eastern china are constrained to be about 250 5 and 7 5 1 0 respectively this is consistent with mantle like protoliths for granitoid rocks and thus precludes the possibility that the a type granites is derived from the anatexis of the 18 o rich upper crust however recycling of crustal materials by earlier subduction cannot be excluded in the processes of generating the a type granitic magmas the variation in the ddepletion of the granites with latitude implies that the paleogeographic localities of the a type granites have not changed significantly since the mesozoic q 2000 elsevier science b v all rights reserved

two phase southward subduction of the mongol okhotsk oceanic plate constrained by permian jurassic granitoids in the erguna and xing an massifs ne china abstract geodynamics of the mongol okhotsk oceanic plate southward subduction are still pending problems this paper presents new zircon la icp ms u pb age and whole rock geochemical data for the middle permian to middle jurassic granitoids in the western erguna and central xing an massifs 267 264 ma 241 ma and 173 ma i type granites and 216 ma a type granites were identified in the erguna and xing an massifs ne china the i type granites were produced by partial melting of the lower mafic crust the 216 ma a type granites were derived from partial melting of crustal materials with tonalitic to granodioritic compositions the 267 264 ma and 241 ma i type granites were generated in an andean type arc setting wheras the 216 ma a type and 173 ma granites were formed in supra subduction extensional setting we summarized previous age data of the middle permian to middle jurassic magmtaic rocks in the erguna and xing an massifs and identified two isolated phases of magmatic activity including the ca 267 225 ma and ca 215 165 ma periods with a significant magmatic gap at ca 225 215 ma these middle permian to middle jurassic magmatic rocks are closely related to the southward subduction of the mongol okhotsk ocean a two stage tectonic evolutionary model was proposed to account for these geological observations in the erguna and xing an massifs involving permian to middle triassic continuous southward subduction of the mongol okhotsk oceanic plate and late triassic to jurassic slab rollback and supra subduction extension

highly fractionated late triassic i type granites and related molybdenum mineralization in the qinling orogenic belt geochemical and u pb hf and re os isotope constraints abstract we present new data on the highly fractionated late triassic i type liyuantang granite which is located in the middle segment of the south qinling subzone of central china and is associated with molybdenum mineralization zircon u pb dating indicates that the granite was emplaced at 210 1 1 9 ma with a single zircon containing an inherited core that yielded an age of 449 8 7 1 ma magmatic zircons from the granite have e hf t values of 4 0 to 1 5 whereas the inherited zircon core has a e hf t value of 5 3 calculated hf model ages of crust formation are indicative of substantial contributions from melting of proterozoic crust that ranges in age from 1501 to 1155 ma the granite contains high concentrations of si al na and k is enriched in rb th and u has elevated rb sr and ga al ratios and is depleted in ti fe mn mg ca and p with significantly negative eu anomalies eu 0 33 0 50 similar to other highly fractionated i type granites these data indicate that the magmas that formed the liyuantang pluton were produced during partial melting of proterozoic garnet absent quartz amphibolites the magmas then fractionated apatite feldspar ti bearing phases biotite and hornblende prior to emplacement re os isotope analysis of molybdenite from the study area yields a mineralization age of 200 9 6 2 ma suggesting that the liyuantang molybdenum deposit formed during a previously unrecognized mineralization event the present results together with previous data demonstrate that highly fractionated i type granites associated with the second pulse of magmatism in the south qinling subzone should be considered highly prospective for mineral exploration focusing on triassic early jurassic granitoids

geochemistry and zircon u pb hf isotopic systematics of the ningshan granitoid batholith middle segment of the south qinling belt central china constraints on petrogenesis and geodynamic processes abstract the ningshan granitoid batholith ngb is located in the middle segment of the south qinling belt sqb section of the qinling orogenic belt in shaanxi province china and consists of the laocheng yanzhiba and lanbandeng intrusions the laocheng intrusion is dominated by quartz diorites granodiorites and monzogranites with the yanzhiba intrusion being granodiorite dominated and the lanbandeng intrusion predominantly consisting of two mica monzogranites la icp ms zircon u pb isotopic dating indicates that the ngb formed during two distinct episodes of magmatism with an earlier episode at 222 216 ma and a later episode at 210 ma whole rock geochemistry and geochronology data have allowed us to divide the ngb into three groups with group 1 rocks consisting of laocheng intrusion quartz diorites and granodiorites and yanzhiba intrusion granodiorites that were produced in the early magmatic episode group 1 samples have high k calc alkaline compositions and are characterized by high mg values high sr cr and ni concentrations and high la yb n and sr y ratios but low yb and y concentrations implying that these rocks were formed from a mixed magma derived from melting of neoproterozoic crustal basaltic rocks and magmas sourced from a region of depleted mantle group 2 rocks are composed of the mid k calc alkaline monzogranites in the laocheng intrusion that were formed in the later magmatic episode and are characterized by lower mg values and lower cr ni and co concentrations than the group 1 samples but with high sr concentrations and la yb n and sr y ratios low y and yb concentrations negligible eu anomalies and a significant range in zircon ehf t values the highest zircon ehf t values of the group 2 samples plot close to the depleted mantle evolutionary line indicating that these rocks were derived from a mixed magma with both crustal and mantle derived components group 3 samples consist of high k calc alkaline two mica monzogranites of the lanbandeng intrusion that were formed during the later magmatic episode these rocks are characterized by high sio2 al2o3 and k2o concentrations with low mgo and sr concentrations low la yb n and sr y ratios nb ta p and ti depletions and significantly negative eu anomalies implying that the magmas from which these rocks formed were derived from partial melting of sedimentary rocks and minor amount of basalt the early magmatic episode associated with formation of the ngb occurred in a continental arc environment at 222 216 ma with 210 ma magmatism during a geodynamic transition from syn collisional to post collisional tectonics across the sqb

granitic rocks as a source of granite the gosta and sundsta granites south west sweden granites among them three generations of microline rich granites intruded repeatedly between 1600 and 900 ma in the south western swedish gneiss complex the deformed and metamorphosed gosta and sundsta granites are medium grained pale greyish red rocks belonging to the oldest generation of microclinerich granites

cretaceous and tertiary sedimentary magmatic and tectonic evolution of north central sonora arizpe and bacanuchi quadrangles northwest mexico the arizpe and bacanuchi quadrangles provide a geologic history representative of the north central part of sonora where lithologies are dominated by late mesozoic and cenozoic igneous rocks in this study new geologic mapping 40ar 39ar dating and geochemical analyses have been combined to provide a stratigraphic framework for this area ten lithostratigraphic units and several igneous and tectonic events can be recognized the oldest outcropping rocks are lower cretaceous strata of the bisbee group which along with the picacho conglomerate record a middle cretaceous compressive tectonic event and associated sedimentation laramide igneous activity is widespread and represented by 1 highly altered andesitic flows and volcaniclastic rocks arroyo alcaparros andesitic rocks of late campanian to maastrichtian age 2 less altered andesitic and dacitic flows cerro las jarillas volcanic rocks of late paleocene age and the intrusive bodies of 3 sierra el manzanal granodiorite and 4 rancho vaqueria quartz monzonite the sierra el manzanal granodiorite was emplaced at ca 68 ma on the basis of a 40ar 39ar biotite age 67 97 0 19 ma and cooled relatively rapidly according to less precise 40ar 39ar hornblende and k feldspar ages from the same sample 64 8 1 0 ma and 62 8 0 3 ma respectively the cerro las jarillas volcanic rocks are slightly younger 40ar 39ar biotite age of 58 67 0 17 ma the rancho vaqueria quartz monzonite was emplaced at ca 57 ma 40ar 39ar biotite age of 56 73 0 14 ma and a less precise 40ar 39ar hornblende age of 55 0 0 7 ma a protracted cooling history of this pluton is indicated by the age spectrum of k feldspar from the same sample a probable magmatic lull and denudation seem to have occurred between middle and late eocene time and probably until the early oligocene subsequently rhyolitic to mafic volcanism began close to late oligocene time and lasted until the early miocene felsic volcanism is represented by the cerro cebadehuachi volcanic rocks from which 40ar 39ar hornblende ages of 27 25 0 09 and 27 32 0 06 ma and a biotite age of 26 97 0 06 ma were obtained at three different localities the mesa pedregosa volcanic rocks represent the transition to younger mafic volcanic activity that occurred during the late oligocene as indicated by a sanidine 40ar 39ar age of 25 48 0 05 ma this late oligocene and early miocene magmatism was paired by two episodes of extensional deformation the first phase is characterized by northwest striking normal faults and folds which expose the deepest structural levels of the area and by the related basin fill the bacanuchi conglomerate the second phase is represented by north striking normal faults and by the syntectonic basin fill the arizpe conglomerate basaltic andesite volcanic flows at the base of the arizpe conglomerate yielded 40ar 39ar whole rock ages of 23 52 0 17 and 21 0 20 ma the extensional deformation 27 to 23 ma in the study area is coeval with the development of metamorphic core complexes in neighboring areas of sonora and with the onset of extension in southern sonora the mafic volcanic rocks and clastic sedimentary units associated with this extension resemble the basin fills that in other parts of sonora are assigned to the baucarit formation geochemical information from samples representing each of the igneous events displayed high k calc alkalic and mostly metaluminous compositions the older units including the arroyo alcaparros andesitic rocks the cerro las jarillas volcanic rocks the sierra el manzanal granodiorite and the rancho vaqueria quartz monzonite are characterized by steep chondrite normalized ree rare earth element slopes and generally well developed negative eu anomalies suggesting garnet and plagioclase removal in the source the younger igneous events including the cerro cebadehuachi and mesa pedregosa volcanic rocks and the basaltic flows associated with the arizpe conglomerate showed basin shaped ree slopes with no eu anomalies suggesting clinopyroxene or amphibole fractionation

petrogenesis of coexisting high silica aluminous and peralkaline rhyolites from yunshan yongtai southeastern china abstract the late cretaceous bimodal yunshan yongtai volcanics in fujian province contain peralkaline rhyolites the only presence of such rhyolites in southeastern china whole rock and mineral chemical compositions are analyzed for the coexisting aluminous metaluminous to weakly peraluminous peralkaline high silica rhyolites from the yunshan volcanics they are sparsely porphyritic and contain k feldspar ferromagnesian minerals quartz magnetite and titanomagnetite phenocrysts as well as accessory minerals such as fayalite chevkinite apatite and zircon the mineral assemblage indicates an oxidizing pre eruption condition these rhyolites exhibit diagnostic geochemical features of a type granites such as elevated 10 4 ga al mostly greater than 2 6 and feo t feo t mgo ratios enrichment in high field strength elements hfse such as zr 400 ppm and nb and strong depletion in al 2 o 3 2 o poor meta granitic igneous rocks in the deep crust and cannot be fractionated from the coeval yunshan mafic magmas geochemical variations of major and trace elements indicate the possible fractionation of k feldspar calcium rich pyroxene fe ti oxides and minor chevkinite during the magma evolution in peralkaline rhyolites we found that the pre existing fe ti oxide and hedenbergite phenocrysts had been transformed into aegirine oxide and aegirine oxide fluorite assemblages respectively these mineral assemblages are the products of the subsolidus reaction of pre existing phenocrysts and extraneous na f rich fluids such na f rich fluids may be derived from the degassing of the subvolcanic rocks the reactions indicate that the yunshan peralkaline rhyolites could be generated through the reaction of highly fractionated aluminous silica magmas and na f rich fluids

early cretaceous lower crustal reworking in ne china insights from geochronology and geochemistry of felsic igneous rocks from the great xing an range this paper presents new zircon la icp ms u pb ages and whole rock geochemical data for two granitic plutons and rhyolites of the baiyingaolao formation in the western xing an range ne china the two syenogranite granitic plutons yield identical zircon u pb age of 142 1 ma and the baiyingaolao rhyolites yield zircon u pb age of 138 2 ma the granites contain some hornblendes and show low zr and zr nb ce y contents and low a cnk 0 98 1 11 mg 6 55 and feot mgo values rhyolite samples show similar geochemical characteristics with a cnk of 0 99 1 10 and mg of 14 21 in combination with the high k2o contents 4 43 5 61 wt and negative correlations between p2o5 and sio2 both the granites and rhyolites were classified as high k calc alkaline i type granitoids all samples give high zirconium saturation temperature of 794 964 c with few initially inherited zircons and belong to high temperature i type granitoids they were generated by dehydration melting of biotite muscovite from sub alkaline meta basalts in lower crust depth leaving garnet amphibole and plagioclase as the major residual minerals the syenogranites and rhyolites are likely formed in mongol okhotsk oceanic subduction setting incorporating other lower crust originated felsic rocks in erguna and xing an massifs and songliao basin it is argued that lower crustal reworking is pronounced in ne china during early cretaceous

in situ zircon u pb and hf o isotopic results for ca 73 ma granite in hainan island implications for the termination of an andean type active continental margin in southeast china abstract we report in the paper integrated analyses of in situ zircon u pb ages hf o isotopes whole rock geochemistry and sr nd isotopes for the longlou granite in northern hainan island southeast china sims zircon u pb dating results yield a crystallization age of 73 ma for the longlou granite which is the youngest granite recognized in southeast china the granite rocks are characterized by high sio2 and k2o weakly peraluminous a cnk 1 04 1 10 depletion in sr ba and high field strength elements hfse and enrichment in lree and large ion lithophile elements lile chemical variations of the granite are dominated by fractional crystallization of feldspar biotite ti fe oxides and apatite their whole rock initial 87sr 86sr ratios 0 7073 0 7107 and end t 4 6 to 6 6 and zircon ehf t 5 0 to 0 8 values are broadly consistent with those of the late mesozoic granites in southeast china coast zircon 18o values of 6 9 8 3 suggest insignificant involvement of supracrustal materials in the granites these granites are likely generated by partial melting of medium to high k basaltic rocks in an active continental margin related to subduction of the pacific plate the ca 73 ma longlou granite is broadly coeval with the campanian ca 80 70 ma granitoid rocks in southwest japan and south korea indicating that they might be formed along a common andean type active continental margin of east southeast asia tectonic transition from the andean type to the west pacific type continental margin of southeast china likely took place at ca 70 ma rather than ca 90 85 ma as previously thought

petrogenesis of the yupo w bearing and dali mo bearing granitoids in the dayaoshan area south china constraints of geochronology and geochemistry abstract the geological significance of early paleozoic caledonian magmatism and associated mineralization in south china is as yet poorly understood compared to the well documented mid late mesozoic yanshanian magmatism and associated mineralization the early paleozoic granitoids were previously thought to be rarely mineralized both caledonian granitoids and yanshanian granitoids occur in the dayaoshan area from the qin hang metallogenic belt south china zircon u pb ages of granodiorite at the yupo skarn w deposit and the monzonite and granodiorite at the dali porphyry mo deposit all i type granites analyzed by sensitive high resolution ion micro probe shrimp and or laser ablation inductively coupled mass spectrometry la icp ms are 441 9 1 9 ma 2 104 6 1 6 ma 2 and 105 3 1 4 ma 2 respectively both elevated zircon 18 o v smow values 5 8 7 7 and negative e hf t values 3 2 to 0 2 indicate that these plutons formed via partial melting of a mesoproterozoic continental crust with minor mantle materials the caledonian w bearing yupo granodiorite is relatively reduced fmq 0 57 whereas the yanshanian mo bearing granodiorite at dali fmq 1 11 is more oxidized than the associated ore barren monzonite fmq 0 52 thus it is likely that the contrasting mineralization between the two plutons was controlled by redox states of granitic magmas

zircon u pb ages geochemistry and sr nd isotopes of the golshekanan granitoid urumieh dokhtar magmatic arc iran evidence for partial melting of juvenile crust

petrogenesis of the mesozoic shuikoushan peraluminous i type granodioritic intrusion in hunan province south china middle lower crustal reworking in an extensional tectonic setting abstract the mesozoic shuikoushan granitoid intrusion in the jiangnan orogen between the yangtze and the cathaysia blocks in southern hunan province south china provides an opportunity to probe deep crustal composition and structure and to investigate the geodynamic evolution of south china the intrusion is composed of granodiorite with i type geochemical affinities and contains zircon with an u pb concordant age of 158 3 1 2 ma rocks from the intrusion have variable sio2 from 58 4 wt to 65 2 wt al2o3 from 15 0 wt to 17 2 wt tio2 from 0 57 wt to 0 76 wt and p2o5 from 0 27 wt to 0 52 wt they have a cnk from 0 97 to 1 23 1 04 on average and are dominantly peraluminous they are characterized by enrichment in lree la sm n 3 47 5 19 and lil e g k rb and depletion in hfse e g u th in primitive mantle normalized trace element diagrams these geochemical features indicate that the rocks are i type granodiorites and have undergone extensive fractional crystallization of hornblende biotite titanite and apatite all samples show negative ehf t 10 6 to 8 1 and end t 5 92 to 6 13 values with relatively high initial 87sr 86sr isr 0 7101 0 7102 and 18o ratios 8 4 9 7 these values significantly differ from mantle values suggesting that they are generated by the amphibole dehydration melting of a mafic source in the middle to lower crust beneath the jiangnan orogen the emplacement of the shuikoushan granitoid intrusion is contemporaneous with the late jurassic to early cretaceous extension within the shi hang rift zone indicating that it may have been formed under an extensional regime in response to both the pacific superplume activity and westward subduction of the pacific plate the extensional processes along with asthenosphere upwelling and basaltic underplating may have triggered the widespread late jurassic granitoid intrusion in southern hunan province and possibly in south china

geological evolution of the volcanic island la gomera canary islands from analysis of its geomorphology abstract erosion and landslide processes played an important role in shaping the geomorphology of the canary islands but for the heavily eroded la gomera island those processes have been unclear we conducted an integrated study of its offshore extension onshore geology and links between them in order to determine the geomorphological evolution of the island relative to the rest of the archipelago the characteristics of the island s barrancos and its interfluves have led us to differentiate four types of morphological areas whose fluvial networks are in different stages of evolution those barrancos offshore are interrupted by la gomera s shelf and its erosion has been much greater than for the rest of the canary islands such erosion is both a function of time and varied swell action la gomera s insular slope is carved by a system of submarine canyons and channels that have morphology indicative of turbidity current erosion many of the barrancos onshore and the canyons offshore have steps or knickpoints some are the result of varied resistance to erosion and others are explained by other mechanisms a ridge whose crest is covered by cone like shape structures is interpreted as of volcanic origin with the particularity that it lacks onshore continuation the opposite of what has been observed elsewhere in the canary islands also in contrast with the other islands of the archipelago la gomera s margin does not seem to have resulted from destructive mass wasting and the only offshore sign of catastrophic events are the presence of two embayments along la gomera s northern shelf edge and a lobe structure on the insular apron at 3000 m depth these features may be the remains of the catastrophic failures that took place on the island 9 4 8 7 ma ago alternatively they could be due to recent catastrophic failures on the upper slope due to sediment steeping since the conclusion of the main volcanic activity 4 0 ma ago la gomera has been intensively eroded by gradual fluvial denudation and secondary failures la gomera s insular margin reveals much regarding its evolution but more comprehensive studies including seismic and coring are needed to understand its whole geological history

petrogenesis of cretaceous shoshonitic rocks in the northern wuyi mountains south china a result of the roll back of a flat slab abstract potassic magmatism is commonly linked to post late orogenic environments such as foundering or convection thinning of continental lithosphere their petrogenesis is crucial for constraining the chemical and physical properties of the remnant sub continental lithospheric mantle here we report new shrimp zircon u pb ages whole rock geochemical results and sr nd and zircon hf isotope data from four potassic plutons the da an yingcheng zixi and honggong plutons in the northern wuyi mountains south china shrimp u pb zircon analyses indicate that these potassic rocks formed at 139 126 ma they are characterized by high sio 2 56 73 and k 2 o 3 8 6 7 with a k 2 o na 2 o ratio of 2 18 2 04 plotting within the field of high sio 2 shoshonites their i sr and end t values vary from 0 7077 to 0 7162 and 5 66 to 10 52 respectively the initial zircon ehf t values range from 2 3 to 13 1 corresponding to t dm modal ages between 707 and 1330 ma these geochemical and isotope characteristics indicate that these shoshonites derived from a subduction modified ancient subcontinental lithospheric mantle and then underwent significantly fractional crystallization of k feldspar plagioclase and accessory minerals such as apatite and fe ti oxides during magma ascent we interpret that asthenospheric mantle upwelling caused by eastward roll back of a flat slab triggered partial melting of the metasomatized lithospheric mantle to result in the early cretaceous shoshonitic magmatism in the northern wuyi mountains an integration of our new results with compiled data from the interior of the south china block reveals that the arc like geochemical signature is confined to the wuyi mountains region but becomes little or even invisible toward inland in south china this implies that the far field effects of the early mesozoic subduction only reached the wuyi mountains ca 500 km away from the trench consistent with flat or shallow subduction models

u pb shrimp ii lu hf isotope and trace element geochemistry of zircons from high grade metamorphic rocks of the irkut terrane sharyzhalgay uplift implications for the neoarchaean evolution of the siberian craton abstract this paper presents new data on the bulk rock composition petrogenesis and u pb zircon ages of high grade metamorphic rocks and granitoids of the irkut terrane which is part of the sharyzhalgay basement uplift located at the southwestern margin of the siberian craton our results allowed us to reliably constrain the neoarchaean evolution of the southwestern siberian craton the high grade rocks under study are two pyroxene amphibole mafic granulites and orthopyroxene bearing intermediate felsic granulites both types of granulite are enriched in ba th and lree and both show clear nb depletion characteristics that are typical of subduction related volcanic rocks the mafic and felsic granulites contain magmatic zircons of 2698 9 ma and 2662 16 ma respectively indicating that most of the protoliths of the high grade rocks formed in the neoarchaean the variable values of end 4 8 to 1 2 whole rock and ehf 1 6 to 2 4 zircons suggest contribution of older crust in the genesis of intermediate felsic granulites the relicts of ca 3 4 ga older rocks have recently been recognized within the irkut high grade metamorphic complex the petrological geochemical and isotopic features of high grade rocks are indicative of their protolith formation in a subduction related setting at the margin of an older continental block the metamorphic zircons in the high grade rocks with ages of 2567 6 and 2540 10 ma and the zircons in the gneissic granitoids with an age of 2540 11 ma probably record neoarchaean collisional events in the irkut terrane the coeval metamorphism ca 2 6 ga and granitoid magmatism ca 2 54 ga in the irkut and kitoy high grade terranes of the sharyzhalgay uplift suggest their neoarchean collision which resulted in the assembly of the sharyzhalgay superterrane similarly amalgamation of the ancient core of the siberian craton which consisted of the west aldan daldyn terranes and the two high grade terranes of the sharyzhalgay uplift probably began in the neoarchaean and was completed by 2 0 to 1 85 ga

chemical and sr nd isotopic compositions and zircon u pb ages of the birimian granitoids from ne burkina faso west african craton implications on the geodynamic setting and crustal evolution abstract the west african craton was the site of massive juvenile crustal addition in the early proterozoic during the eburnean orogeny 2 1 ga in this study we determined chemical and isotopic compositions as well as zircon u pb ages of granitoid samples from ne burkina faso these data were then used to constrain the chemical characteristics emplacement age and tectonic environment of these rocks in the context of the west african craton evolution birimian paleoproterozoic granitoids of ne burkina faso are associated with volcanic and volcano sedimentary sequences of the greenstone belts analyses indicate that the na rich birimian granitoids of tonalite trondhjemite granodiorite ttg composition were generated by partial melting of a garnet bearing amphibolite crust granite intrusions derived from partial re melting of the deep basement of felsic calc alkaline nature with contribution of metasediments zircon u pb isotopic analyses yielded ages between 2122 15 ma and 2181 7 ma for the birimian na rich granitoids and 2151 10 ma for a biotite granite ij10 sr nd isotopic data show very low initial sr composition i sr t 0 7007 positive epsilon neodymium values nd t 0 7 to 2 5 and sm nd model ages t dm of 2363 2558 ma these data are similar to those of mafic rocks of the pissila greenstone belt i sr t 0 7003 0 7015 nd t 3 2 to 4 1 t dm 2336 2552 ma and further suggest that the na rich granitoids are of juvenile nature the present study together with published data on the birimian volcanics and meta sedimentary rocks of the west african craton preclude contamination of the juvenile birimian rocks of ne burkina faso by reworked archean materials the birimian granitoids of ne burkina faso were mostly emplaced during the early stage 2 19 2 15 ga of a large scale crustal growth event 2 2 2 0 ga where large amount of juvenile materials were added to the crust from the depleted mantle in a tectonic environment comparable to modern volcanic arcs

geochemistry and zircon geochronology of the i type high k calc alkaline and s type granitoid rocks from southeastern roraima brazil orosirian collisional magmatism evidence 1 97 1 96 ga in central portion of guyana shield abstract the understanding of the geological evolution of the uatuma anaua domain in southeastern roraima central region of guyana shield is of major significance in the study of the amazonian craton this region lies between some major paleoproterozoic geological geochronological provinces tapajos parima or ventuari tapajos dominant maroni itacaiunas or transamazon northwest and central amazonian or central amazon southeast and east geological mapping of the northern area of uatuma anaua domain integrated with whole rock geochemistry data and previous and new pb evaporation and u pb zircon geochronology point out for a plutonic collisional magmatic event 1975 1968 ma represented by i type high k calc alkaline martins pereira and s type serra dourada granitoid rocks this magmatism was probably generated from crustal sources by partial melting during amalgamation of the ttg like anaua magmatic arc 2028 ma with transamazonian 2 2 2 0 ga and central amazonian older than 2 3 ga terranes local cumulatic leucogranites fills planar structures of the martins pereira granites these leucogranites show younger ages 1909 ma and several inherited zircons 2354 2134 1997 and 1959 ma suggesting origin from crustal sources

seismological evidence for a delamination process in the lithosphere under the alboran sea summary the continental collision between the african and eurasian plates in the iberian peninsula is solved with a nw se compression with an extensional basin the alboran sea to explain this paradox several models have been proposed including the subduction process of a lithospheric plate in this study a relocation of the seismicity of the area using a jhd algorithm for the period 1950 1995 has been performed which shows a specific hypocentre pattern that is not compatible with plate subduction in addition the direction of the stresses acting in the area has been determined through a comprehensive study of all existing focal mechanisms together with calculations for 19 new earthquakes with sufficient data to determine the focal solution after considering all these data the absence of intermediate shocks in the central part of the alboran basin and the predominantly thrusting mechanisms at the borders of the basin with pressure axes perpendicular to the front we consider a delamination process as a possible mechanism acting in the area

geology and petrology of the simav magmatic complex nw anatolia and its comparison with the oligo miocene granitoids in nw anatolia implications on tertiary tectonic evolution of the region the oligo miocene granitic plutons and their related volcanic subvolcanic successions form a nw se trending magmatic belt along the northern border of the menderes massif this belt evolved within a nappe package consisting of the menderes metamorphics sakarya continent afyon zone and tavsanli zone and also intruded this nappe package the ezine evciler eybek kozak alacam koyunoba egrigoz and the baklan plutons emplaced along this belt and show similarities in their internal structures emplacement mechanisms and petrological characteristics these different granitic plutons cut and stitch various combinations of the nappe package of the above mentioned tectonic belts and evolved during and following the alpine collision they all show characteristic map patterns of shallow seated plutons and range from granite to monzogranite the granitic plutons display calc alkaline i type and post collisional geochemical characteristics the egrigoz koyunoba plutons and their subvolcanic volcanic phases simav magmatic complex were studied in detail the geochemical characteristics and field occurences of the simav magmatic complex were compared to the other magmatic associations in western anatolia and it was determined that it is of collisional origin and not related to an extensional tectonic regime as suggested in some recent studies

lower cretaceous alkali feldspar granites in the central part of the great xing an range northeastern china chronology geochemistry and tectonic implications the mingshui jilasitai suolun area located in the central part of the great xing an range is characterized by large volumes of alkali feldspar granites however the formation time and tectonic setting of these rocks remains controversial owing to a lack of precise geochronological and detailed geochemical data in this paper we report new sims u pb zircon ages and mineralogical petrographical and geochemical data for lower cretaceous alkali feldspar granites from the mingshui jilasitai suolun area the sims zircon dating results indicate that these granites formed at 133 6 135 9 ma the mineralogical petrographical and geochemical data show that these granitic rocks belong to highly fractionated i type granites combined with the regional geology data we propose that the formation of the lower cretaceous alkali feldspar granitic rocks was related to an extension induced by delamination of the lithosphere that arose from subduction of the palaeo pacific plate

timing and genesis of the adakitic and shoshonitic intrusions in the laoniushan complex southern margin of the north china craton implications for post collisional magmatism associated with the qinling orogen abstract the nww striking qinling orogen formed in the triassic by collision between the north china and yangtze cratons triassic granitoid intrusions mostly middle to high k calc alkaline are widespread in this orogen but contemporaneous intrusions are rare in the southern margin of the north china craton an area commonly considered as the hinterland belt of the orogen in this paper we report zircon u pb ages elemental geochemistry and sr nd hf isotope data for the laoniushan granitoid complex that was emplaced in the southern margin of the north china craton zircon u pb dating shows that the complex was emplaced in the late triassic 228 1 to 215 4 ma indicating that it is part of the post collisional magmatism in the qinling orogen the complex consists of from early to late biotite monzogranite quartz diorite quartz monzonite and hornblende monzonite which span a wide compositional range e g sio2 55 9 70 6 wt k2o na2o 6 6 10 2 wt and mg of 24 to 54 the biotite monzogranite has high al2o3 15 5 17 4 wt sr 396 1398 ppm and ba 1284 3993 ppm contents and relatively high la yb mostly 14 30 and sr y mostly 40 97 ratios but low yb mostly 1 3 1 6 ppm and y mostly14 19 ppm contents features typical of adakitic rocks the quartz monzonite hornblende monzonite and quartz diorite have a shoshonitic affinity with k2o up to 5 58 wt and k2o na2o ratios averaging 1 4 the rocks are characterized by strong lree hree fractionation in chondrite normalized ree pattern without obvious eu anomalies and show enrichment in large ion lithophile elements but depletion in high field strength elements nb ta ti the biotite monzogranite 228 ma has initial 87sr 86sr ratios of 0 7061 to 0 7067 end t values of 9 2 to 12 6 and ehf t values of 9 0 to 15 1 whereas the shoshonitic granitoids mainly 217 215 ma have similar initial 87sr 86sr ratios 0 7065 to 0 7075 but more radiogenic end t 12 4 to 17 0 and ehf t 14 1 to 17 0 the sr nd hf isotope data indicate that the rocks were likely generated by partial melting of an ancient lower continental crust with heterogeneous compositions as partly confirmed by the widespread presence of early paleoproterozoic inherited zircons mafic microgranular enclaves mmes characterized by fine grained igneous textures and an abundance of acicular apatites are common in the laoniushan complex compared with the host rocks they have lower sio2 48 6 53 7 wt and higher mg 51 56 cr 122 393 ppm and ni 24 79 ppm but equivalent sr nd isotope compositions indicating that the mmes likely originated from an ancient enriched lithospheric mantle the abundance of mmes in the granitoid intrusions suggest that magma mixing plays an important role in the generation of the laoniushan complex collectively it is suggested that the laoniushan complex was a product of post collisional magmatism related to lithospheric extension following slab break off formation of the adakitic and shoshonitic intrusions in the laoniushan complex indicates that the qinling orogen had evolved into a post collisional setting by about 230 210 ma