depleted mantle source for the ulungur river a type granites from north xinjiang china geochemistry and nd sr isotopic evidence and implications for phanerozoic crustal growth abstract the ulungur river granites from north xinjiang china display two petrological trends 1 a peralkaline trend composed of alkali amphibole and alkali pyroxene bearing granites and dykes and 2 an aluminous trend represented by alkali granites monzogranites and aluminous granite dykes within the peralkaline granites rb sr whole rock isochron dating yielded an age of 300 ma for the emplacement of the peralkaline granites and 270 ma for the aluminous granites the ulungur river granites share all the geochemical features common to a type granites of the world the ulungur river granites are post orogenic and emplaced in a post collisional extensional environment the peralkaline and aluminous rocks have indistinguishable nd isotopic compositions they have unusually positive and relatively uniform nd t values ranging from 5 1 to 6 7 for the peralkaline rocks at 300 ma and from 5 5 to 5 9 for the aluminous rocks at 270 ma the initial 87sr 86sr ratios cannot be determined precisely by the whole rock isochron technique mainly because most samples are highly radiogenic and have high rb sr ratios in addition the large variation in sr isotopic compositions can partly be explained by crustal contamination during magma differentiation the nd isotopic data clearly indicate that both the peralkaline and aluminous rocks were derived from a long lived depleted mantle reservoir the formation of the ulungur river a type granites is hypothesized as follows 1 a depleted mantle was first metasomatised then subjected to partial melting leading to the generation of basic magmas now represented by the kalatongke mafic ultramafic complex in the ulungur river area 2 the basic magmas have undergone high degrees of fractional crystallisation with separation of biotite hornblende plagioclase potassium feldspar and other accessory phases such as apatite and ilmenite with the residual magmas forming the peralkaline granites during the magmatic differentiation the liquids were probably contaminated by crustal materials as evidenced by nb depletion and nd sr isotopic systematics on the other hand the formation of aluminous granites involved a replenishment of new mantle derived magmas into the differentiating magma chamber and followed by fractional crystallisation with retention of hydrous phases hornblende and biotite the petrological evolution of the ulungur river granites is thus from peralkaline to calc alkaline and not from calc alkaline to peralkaline as more often observed elsewhere the ulungur river granites in common with the voluminous granitoids occurring in the central asian orogenic belt represent a significant juvenile addition of the continental crust in the phanerozoic

highly fractionated i type granites in ne china ii isotopic geochemistry and implications for crustal growth in the phanerozoic ne china is the easternmost part of the central asian orogenic belt caob the area is distinguished by widespread occurrence of phanerozoic granitic rocks in the companion paper part i we established the jurassic ages 184 137 ma for three granitic plutons xinhuatun lamashan and yiershi we also used geochemical data to argue that these rocks are highly fractionated i type granites in this paper we present sr nd o isotope data of the three plutons and 32 additional samples to delineate the nature of their source to determine the proportion of mantle to crustal components in the generation of the voluminous granitoids and to discuss crustal growth in the phanerozoic despite their difference in emplacement age sr nd isotopic analyses reveal that these jurassic granites have common isotopic characteristics they all have low initial 87 sr 86 sr ratios 0 7045f0 0015 positive end t values 1 3 to 2 8 and young sm nd model ages 720 840 ma these characteristics are indicative of juvenile nature for these granites other late paleozoic to mesozoic granites in this region also show the same features sr nd and oxygen isotopic data suggest that the magmatic evolution of the granites can be explained in terms of two stage processes 1 formation of parental magmas by melting of a relatively juvenile crust which is probably a mixed lithology formed by pre existing lower crust intruded or underplated by mantle derived basaltic magma and 2 extensive magmatic differentiation of the parental magmas in a slow cooling environment the widespread distribution of juvenile granitoids in ne china indicates a massive transfer of mantle material to the crust in a post orogenic tectonic setting several recent studies have documented that juvenile granitoids of paleozoic to mesozoic ages are ubiquitous in the central asian orogenic belt hence suggesting a significant growth of the continental crust in the phanerozoic d 2003 elsevier science b v all rights reserved

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

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

plutonic rock types series discrimination of various granitoid series and related rocks abstract the streckeisen qap diagram discriminates four characteristic type series among the large variety of granitoids associated in intrusions three of them integrate varied compositions from basic to acid terms 1 the calcalkaline series with its low k or trondhiemite medium k or granodioritic high k or monzonitic variants 2 the alkaline series with its characteristic syenitic members 3 the tholeiitic series deprived of k feldspars the fourth 4 corresponds to mobilizates associated with migmatites of varied composition but always quartz rich the generalization in the qapf system allowing the plotting of undersaturated alkaline series provides an excellent visual display of the major associations and trends for the plutonic rocks

textural geochronological and chemical constraints from polygenetic titanite and monogenetic apatite from a mid crustal shear zone an integrated epma sims and tims study abstract titanites extracted from a 520 9 ma syn orogenic syenite at otjimbingwe damara orogen namibia show shape colour and u pb systematics that vary with position in the syenite relative to a major shear zone most titanite fractions from syenite cropping out outside the shear zone are characterized by a medium brown anhedral core overgrown by a pale brown subhedral rim empa and sims analyses show that the cores are enriched in al fe and sometimes na mg and mn but also in ree nb and zr relative to the rim tims u pb ages from these titanites gave relatively imprecise 207pb 206pb ages between 680 21 ma and 695 20 ma as well as 570 8 ma to 604 9 ma mainly due to their low 206pb 204pb ratios combined th u pb relationships suggest that these titanites contain a component similar to ca 715 750 ma old titanite populations observed so far only in neoproterozoic syenites from the northern part of the orogen titanites from syenites within the shear zone are dark brown mostly euhedral to subhedral and display only occasionally a pale brown rim these titanites show decreasing concentrations of na mg al and fe and increasing concentrations of mn from core to rim interpreted to reflect growth zonation abundances of mree hree y nb and zr are higher in the rim than in the core 207pb 206pb ages obtained on these titanites range from 470 2 ma to 538 3 ma for most samples only the samples with the highest 206pb 204pb ratios between 350 and 230 have u pb ages similar to the previously published u pb zircon age of 520 9 ma from the same complex other titanite fractions with lower 206pb 204pb ratios have slightly older ages than ca 520 ma indicating some inheritance inherited titanite survived multiple metamorphic episodes in the damara orogen between ca 750 ma and 470 ma and the igneous event that lead to the intrusion of the otjimbingwe syenite at 520 ma these data imply a high closure temperature of u pb in titanite of 650 700 c consistent with previous studies coeval apatite has no apparent inheritance low 206pb 204pb ratios between 55 and 170 and u pb ages similar to or only slightly younger than the u pb zircon or titanite age obtained on the titanite fractions with the highest 206pb 204pb ratios assuming a closure temperature for u pb of 900 c for zircon 700 c for titanite and 450 c for apatite initial fast cooling of the complex can be inferred our data demonstrate that titanite can contain multiple age domains preserving a chronological and chemical record of previous igneous events

petrology and geochemistry of the lyngdal granodiorite southern norway and the role of fractional crystallisation in the genesis of proterozoic ferro potassic a type granites abstract in south western norway the sveconorwegian orogenic thickening 1024 970 ma is followed by an important post collisional magmatism 950 930 ma divided in two suites vander auwera et al 2003 the anorthosite mangerite charnockite suite amc suite and the hornblende biotite granitoids suite hbg suite the hbg suite displays a continuous trend from gabbronorites to granites this paper presents the petrography and geochemistry major and trace elements sr nd isotopes of the lyngdal granodiorite and associated massifs tranevag and red granite massifs which belong to the hbg suite although being very close to the anorthosite massifs mafic microgranular enclaves mme resulting from magma mingling can be abundant and probably correspond to the parent magma of the studied plutons the lyngdal granodiorite and associated massifs are subalkaline metaluminous a type granitoids with high feo t feo t mgo ratio and k 2 o content forming a ferro potassic a type continuous trend from quartz monzodiorite to granite 56 72 wt sio 2 in harker diagrams the lyngdal tranevag plutons share the proterozoic rapakivi granites trend that they extend to lower sio 2 content major and trace element modelling as well as sr nd isotopes show that fractional crystallisation without assimilation is the differentiation process for lyngdal tranevag fractionating minerals are clinopyroxene hornblende plagioclase oxides biotite apatite zircon and allanite the red granite 71 75 wt sio 2 does not belong to this trend probably due to a different initial magma composition this study shows that ferro potassic a type granitoids can be derived by fractional crystallisation from mafic magmas

generation of the early cenozoic adakitic volcanism by partial melting of mafic lower crust eastern turkey implications for crustal thickening to delamination abstract early cenozoic 48 50 ma adakitic volcanic rocks from the eastern pontides ne turkey consist of calc alkaline and high k calc alkaline andesite and dacite with sio2 contents ranging from 56 01 to 65 44 wt this is the first time that early eocene volcanism and adakites have been reported from the region the rocks are composed of plagioclase amphibole quartz and mg rich biotite they have high and low mg values ranging from 55 to 62 and 13 to 42 respectively high mg rocks have higher ni and co contents than low mg samples the rocks exhibit enrichments in large ion lithophile elements including the light rare earth elements depletions in nb ta and ti and have high la yb and sr y ratios their relative high isr 0 70474 0 70640 and low end 50 ma values 2 3 to 0 8 are inconsistent with an origin as partial melts of a subducted oceanic slab combined major and trace element and sr nd isotope data suggest that the adakitic magmas are related to the unique tectonic setting of this region where a transition from a collision to an extension stage has created thickening and delamination of the pontide mafic lower crust at 50 ma the high mg adakitic magmas resulted from partial melting of the delaminated eclogitic mafic lower crust that sank into the relatively hot subcrustal mantle and its subsequent interaction with the mantle peridotite during upward transport leaving garnet as the residual phase elevates the mgo content and mg of the magmas whereas low mg magmas formed by the melting of newly exposed lower crustal rocks caused by asthenospheric upwelling which supplies heat flux to the lower crust the data also suggest that the mafic lower continental crust beneath the region was thickened between the late cretaceous and the late paleocene and delaminated during late paleocene to early eocene time which coincides with the initial stage of crustal thinning caused by crustal extensional events in the eastern pontides and rules out the possibility of an extensional regime before 50 ma in the region during the late mesozoic to early cenozoic

petrogenesis of the late cretaceous demirkoy igneous complex in the nw turkey implications for magma genesis in the strandja zone abstract the srednogorie zone in bulgaria and its eastern continuation in nw turkey the strandja zone consist of a late cretaceous magmatic belt comprised of plutonic volcanic and associated volcano sedimentary rocks the demirkoy igneous complex is the biggest cretaceous pluton within the strandja zone and its age is between 71 and 84 ma the demirkoy pluton and additional smaller plutons are intruded into triassic and older metamorphic basement rocks a contact metamorphic aureole with hornblende hornfels facies conditions was developed around the demirkoy pluton the wnw trending demirkoy pluton has an elliptical shape and a concentrically zoned internal structure in this structure gabbro diorites and quartz diorites are only seen in the sw corner of the pluton while granodiorites form the main body of the pluton surrounded by a zone of granite the granodiorites contain dioritic mafic microgranular enclaves small quartz monzonite lenses and or bodies and mafic dykes are also observed in the demirkoy igneous complex geochemically the demirkoy igneous complex has calc alkaline metaluminous and medium k characteristics there is a significant correlation between the lree hree ratios and sio 2 values chondrite normalized ree patterns are relatively flat la n lu n 2 in gabbros this ratio ranges from 3 to 11 for the diorite granodiorites and from 14 to 35 for the granites dioritic enclaves have ree patterns similar to those of the main body and have la n lu n values between 3 and 6 relatively enriched lile sr k rb ba and th and relatively depleted hfse ta nb and ti values indicate the classic subduction related origin of the complex the initial isotopic signatures range from e nd i 0 45 to 2 57 and 87 sr 86 sr i 0 7042 0 7064 for gabbros and e nd i 0 43 to 2 67 and 87 sr 86 sr i 0 7048 0 7059 for granodiorites and granites 18 o values range from 6 18 to 7 80 vsmow for gabbros and from 6 86 to 8 89 vsmow for granodiorites and granites based on geochemical and isotopic characteristics this magmatic complex can be subdivided into 4 groups a gabbro b diorite to alkali granite main body c syenite monzonite and d mafic dykes geochemical data and modelling results favour a typical subduction related enriched lithospheric mantle and lower crustal source for the demirkoy igneous complex slab derived fluids and crustal contamination also played a key role in the petrogenesis of this magmatic suite

petrology and geochemistry of syn to post collisional metaluminous a type granites a major and trace element and nd sr pb o isotope study from the proterozoic damara belt namibia abstract leucocratic a type granites of the proterozoic damara orogen namibia are a distinctive groups of rocks based on their mineralogical chemical and isotopic characteristics a type granites can be distinguished from the leucocratic s type granites on the basis of fe rich amphibole and biotite and higher abundances of zr nb y and lree but lower values of 87 sr 86 sr 500 ma and 18 o in the a type granites in comparison with a type granites described in the literature the damaran a type granites are enriched in cao al2o3 mgo feo ba sr and eu but depleted in ga and zn low k rb rb sr rb ba and sr ba ratios indicate that these melts are not fractionation products of calc alkaline source rocks and therefore these chemical criteria are interpreted as a feature of the source rocks i e undepleted metatonalites the a type granites have high calculated zircon and monazite saturation temperatures mostly in excess of 800 c and it is concluded that these granites represent high temperature partial melts the relationship between major and trace element data and isotopic composition demonstrates that the a type granites originate from several sources and have undergone different processes the lack of evidence for shallow crustal contamination e g lack of country rock xenoliths the low viscosities of the melts as inferred from their high calculated temperature and their high nd concentrations relative to the country rocks suggest that the isotopic characteristics were acquired from an enriched mantle initial sr isotopic compositions vary over a narrow range 0 70486 0 70928 but the initial nd isotopic compositions vary considerably with initial end values between 0 03 and 6 35 this wide range in the nd isotope values is probably the result of interaction of mantle derived magmas with crustal rocks a type granites at baukwab have negatively correlated initial end values and 207 pb 204 pb and 206 pb 204 pb ratios indicating interaction of mantle derived magmas low initial end low 207 pb 204 pb and 206 pb 204 pb with continental crust high initial end high 207 pb 204 pb and 206 pb 204 pb a type granites from albrechtstal and oetmoed have positively correlated pb isotope ratios and show also positive correlations between nd isotopes and pb isotopes suggesting interaction of at least two different source materials the relationship between nd isotopes and nd concentrations precludes simple assimilation instead mixing of different sources seems to be more realistic for the a type granites from oetmoed oxygen isotopes are negatively correlated with sr isotopes indicating that the crustal end member has high 18 o values and rather low initial 87 sr 86 sr ratios whereas a hypothetical mantle component has lower 18 o values but higher initial 87 sr 86 sr ratios the chemical and isotope data suggest that the damaran a type granites were generated by a variety of processes including partial melting of mantle derived tonalitic sources limited crystal fractionation and interaction of these magmas with crustal material these data indicate that the damaran a type suites mark episodes of continental growth during which mantle material although limited in extent is added to the crust

mineralogy petrography and whole rock geochemistry of the tertiary granitic intrusions in the eastern pontides turkey abstract granitic intrusions in eocene and post eocene volcanic rocks outcrop in the northern and southern zones of the eastern pontides ne turkey intrusions in the northern zone extend nw se whereas those in the southern zone are nearly e w orientated the contacts of the intrusions with the volcanic rocks are sharp epidotized and include volcanic xenoliths the margins of southern zone intrusions often contain abundant angular mafic microgranular enclaves of diorite to quartz diorite composition the rocks also show evidence of mingling and mixing between coeval mafic and felsic magmas field observations suggest a stopping type of ascent and emplacement style for the intrusions petrographically intrusions show variations in both colour and mineralogy with fine to medium granular monzonitic poikilitic rapakivi anti rapakivi and graphic textures based on modal mineralogy the northern rocks are monzonite quartz monzonite monzodiorite and quartz monzodiorite whereas the southern samples are monzogranite and granodiorite the rocks are generally calc alkaline to mildly alkaline transitional and metaluminous and show a cafemic trend the northern zone intrusions form a post collisional a type alkaline monzonitic association and southern zone intrusions form a post collisional i type granodioritic calc alkaline transitional association whole rock compositional data indicate that differentiation occurred via fractional crystallisation with or without magma mixing incompatible and rare earth element patterns indicate that both the northern and the southern zone intrusions were derived from melting of a mantle region enriched by subduction related fluids but evolved differently during ascent and emplacement u pb zircon dating in the southern zone yields an intrusion age of 44 4 0 3 ma regional geodynamics indicates post collisional extensional tectonics in the region crustal involvement and the level of emplacement may have been important for magmatic evolution especially for the southern zone intrusions after the cessation of subduction and subsequent crustal thickening

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

petrogenesis of collision related plutonics in central anatolia turkey central anatolia exhibits good examples of calc alkaline and alkaline magmatism of similar age in a collision related tectonic setting continent island arc collision in the central anatolia region late cretaceous post collisional plutonic rocks intrude palaeozoic mesozoic metamorphic rocks overthrust by upper cretaceous ophiolitic units to make up the central anatolian crystalline complex in the complex three different intrusive rock types may be recognised based on their geochemical characteristics i calc alkaline behrekdag cefalikdag and celebi ii subalkaline transitional baranadag and ii alkaline hamit the calc alkaline and subalkaline plutonic rocks are metaluminous i type plutons ranging from monzodiorite to granite the alkaline plutonic rocks are metaluminous to peralkaline plutons predominantly a type ranging from nepheline monzosyenite to quartz syenite all intrusive rocks show enrichment in lile and lree relative to hfse and have high 87sr 86sr and low 143nd 144nd ratios these characteristics indicate an enriched mantle source region s carrying a subduction component inherited from pre collision subduction events the tectonic discrimination diagram of rb vs y nb suggests that the calc alkaline subalkaline and alkaline plutonic rocks have been affected by crustal assimilation combined with fractional crystallisation processes the coexistence of calc alkaline and alkaline magmatism in the central anatolian crystalline complex may be attributed to mantle source heterogeneity before collision the former carries a smaller intraplate component and pre subduction enrichment compared to the latter either thermal perturbation of the metasomatised lithosphere by delamination of the thermal boundary layer tbl or removal of a subducted plate slab breakoff is the likely mechanism for the initiation of the post collisional magmatism in the complex

cenozoic evolution of neotethys and implications for the causes of plate motions africa north america eurasia plate circuit rotations combined with red sea rotations and new estimates of crustal shortening in iran define the cenozoic history of the neotethyan ocean between arabia and eurasia the new constraints indicate that arabia eurasia convergence has been fairly constant at 2 to 3 cm yr since 56 ma with slowing of africa eurasia motion to 1 cm yr near 25 ma coeval with the opening of the red sea ocean closure occurred no later than 10 ma and could have occurred prior to this time only if a large amount of continental lithosphere was subducted suggesting that slowing of africa significantly predated the arabia eurasia collision these kinematics imply that africa s disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern eurasia slowed its motion the slow steady rate of northward subduction since 56 ma contrasts with strongly variable rates of magma production in the urumieh dokhtar arc implying magma production rate in continental arcs is not linked to subduction rate

acoustic gravity waves interacting with the shelf break 1 a mathematical solution of the two dimensional linear problem of an acoustic gravity wave propagating over a bottom with a step in a slightly compressible ocean is presented expressions for the flow field on both sides of the step are derived furthermore an extended problem is given that provides a solution for a group of acoustic gravity waves generated by a submarine earthquake propagating toward a continental shelf the dynamic bottom pressure produced by the acoustic gravity waves is probably measurable especially at the vicinity of the seaward face of the shelf break where incident and reflected modes appear simultaneously a successful recording of such bottom pressures could assist in the early detection of tsunami

hf isotopes in zircon reveal contrasting sources and crystallization histories for alkaline to peralkaline granites of temora southeastern australia peralkaline granites exhibit the hallmark features of a type igneous rocks but strongly differentiated chemistry and intense hydrothermal alteration camouflage their ultimate origins we present the first in situ hf isotope data from zircons of peralkaline granites aimed at clarifying the protoliths of these plutons and their genetic relationship to associated metaluminous weakly peraluminous granites this study used rocks of the devonian narraburra complex in southeastern australia and found that correlations between hf isotopes and trace element ratios reveal fundamentally different origins for the nonperalkaline and peralkaline granites the latter have a depleted mantle like ancestry whereas a weakly peraluminous rock formed from melts of older arc crust that were modified by interaction with juvenile probably alkaline magmas juxtaposition of crust and mantle derived magmas reflects the high heat flow and lithosphere scale faults associated with continental extension and explains the diversity of a type granites

petrology and geochemistry of late stage intrusions of the a type mid proterozoic pikes peak batholith central colorado usa implications for petrogenetic models abstract the 1 08 ga anorogenic a type pikes peak batholith front range central colorado is dominated by coarse grained biotite amphibole syenogranites and minor monzogranites collectively referred to as pikes peak granite ppg the batholith is also host to numerous small late stage plutons that have been subdivided into two groups e g wobus 1976 studies in colorado field geology colorado school of mines professional contributions colorado 1 a sodic series sio 2 44 78 wt k na 0 32 1 36 composed of gabbro diabase syenite quartz syenite and fayalite and sodic amphibole granite and 2 a potassic series sio 2 70 77 wt k na 0 95 2 05 composed of biotite granite and minor quartz monzonite differences in major and trace element and nd isotopic characteristics for the two series indicate different petrogenetic histories potassic granites of the late stage intrusions appear to represent crustal anatectic melts derived from tonalite sources based on comparison of their major element compositions with experimental melt products in addition nd isotopic characteristics of the potassic granites e nd 1 08 ga 0 2 to 2 7 overlap with those for tonalites granodiorites ca 1 7 ga boulder creek intrusions e nd 1 08 ga 2 4 to 3 6 exposed in the region some of the partial melts evolved by fractionation dominated by feldspar the late stage potassic granites share geochemical characteristics with most of the ppg which is also interpreted to have an anatectic origin involving tonalitic crust the origin of monzogranites associated with the ppg remains unclear but mixing between granitic and mafic or intermediate magmas is a possibility syenites and granites of the sodic series cannot be explained as crustal melts but are interpreted as fractionation products of mantle derived mafic magmas with minor crustal input high temperature and low oxygen fugacity estimates e g frost et al 1988 american mineralogist 73 727 740 support a basalt fractionation origin as do e nd values for sodic granitoids e nd 1 08 ga 2 2 to 0 7 which are higher than e nd values for colorado crust at 1 08 ga ca 1 0 to 4 0 enrichments in incompatible elements e g rare earth elements rb y and depletions in compatible elements e g cr sr ba in the sodic granitoids compared to coeval mafic rocks are also consistent with fractionation accessory mineral fractionation release of fluorine rich volatiles and or removal of pegmatitic fluids could have modified abundances of ce nb zr and y in some sodic granitoid magmas gabbros and mafic dikes associated with the sodic granitoids have e nd 1 08 ga of 3 0 to 3 5 which are lower than depleted mantle at 1 08 ga and their trace element characteristics suggest derivation from mantle sources that were previously affected by subduction related processes however it is difficult to characterize the mantle component in these magmas because assimilation of crust during magma ascent could also result in their observed geochemical features the pikes peak batholith is composed of at least two petrogenetically different granite types both of which exhibit geochemical characteristics typical of a type granites models proposed for the petrogenesis of the granitoids imply the existence of mafic rocks at depth and addition of juvenile material to the crust in central colorado at 1 1 ga

petrogenesis of the red mountain pluton laramie anorthosite complex wyoming implications for the origin of a type granite abstract the red mountain pluton the youngest intrusion in the laramie anorthosite complex is one of five monzonitic to granitic a type plutons intruded at 1 43 ga in the laramie mountains of southeastern wyoming the red mountain pluton ranges in composition from fayalite monzonite clinopyroxene quartz monzonite and biotite hornblende quartz syenite to granite the red mountain pluton is petrologically and geochemically distinct from the northern and southern sherman batholith the sybille intrusion and the maloin ranch pluton it has higher feo t feo t mgo and higher k 2 o is more strongly enriched in rees and at any given silica content it has lower abundances of tio 2 feo mgo cao and p 2 o 5 the fayalite monzonite in the red mountain pluton crystallized at temperatures around 1000 c and oxygen fugacities 1 2 log units below that of the fmq buffer similar to the crystallization conditions of the sybille and maloin ranch plutons the biotite hornblende quartz syenite crystallized at oxygen fugacities near or slightly below those of fmq most of the units in the pluton carry mantle like nd sr and pb isotopic compositions similar to the least contaminated anorthositic and ferrodioritic rocks of the lac indicating that the pluton evolved mainly via differentiation substantial crustal assimilation occurred only in the late dikes and the granite we suggest that all of the 1 43 ga a type intrusions in southeastern wyoming are ultimately derived from tholeiites extreme differentiation or partial melting produced monzonitic magmas that have assimilated varying amounts of siliceous crust the differences between the red mountain pluton and other a type granitoids in southeastern wyoming are related to the extent of differentiation prior to crustal assimilation the compositional ranges of a type granitoids in southeastern wyoming suggest that the geochemical spectrum of a type granites worldwide similarly are produced from evolved mantle derived melt that has assimilated varying proportions of crustal material

deep ocean water transport by acoustic gravity waves acoustic gravity waves are compression type waves propagating with amplitudes governed by the restoring force of gravity they are generated among others by wind wave interactions surface waves interactions and submarine earthquakes we show that acoustic gravity waves contribute to deep ocean currents and circulation they cause chaotic flow trajectories of individual water parcels which can be transported up to a few centimeters per second

generation of metaluminous a type granites by low pressure melting of calc alkaline granitoids melting experiments on two calc alkaline rocks a tonalite and a granodiorite demonstrate that shallow dehydration melting of hornblende and biotite bearing granitoids generates metaluminous a type granitic melts profuse crystallization of calcic plagioclase orthopyroxene during low pressure p 4 kbar incongruent melting explains all of the major and trace element characteristics of a type granites e g their low al ca mg sr and eu contents and high ga al and k na ratios as well as their common association with anorthositic and mangeritic rocks the residual assemblage produced during melting of the same rocks in the deep crust p 8 kbar is dominated by clinopyroxene and as a consequence most of the chemical features diagnostic of a type granites are lost the high temperatures 900 c and low h 2 o contents 4 wt that are characteristic of a type magmas are adequately explained by the h 2 o poor nature of the granitoid source materials and require neither a granulitic nor a f rich source previous attempts to explain the origin of a type granites have focused on the nature of the source material these experiments show that pressure of melting is at least as important as source composition in engendering a type melts

the hohonu batholith of north westland new zealand granitoid compositions controlled by source h 2 o contents and generated during tectonic transition geochemical studies on the hohonu batholith of the west coast south island new zealand have recognised two distinct but chemically related suites of mid cretaceous granitoids the suites are characterised by restricted radiogenic isotopic compositions sr i 0 7062 to 0 7085 nd i 4 4 to 6 1 and represent melting of a mafic lithosphere source followed by interaction with ordovician metasediments the two suites te kinga suite and deutgam suite are distinguished by contrasting contents of al2o3 na2o sr ba eu and hree attributable to different residual asssemblages controlled by differing h2o contents during melting of a metabasaltic source the relatively mafic metaluminous i type deutgam suite represents magmas derived by dehydration melting in equilibrium with an amphibolitic plagioclase amphibole residue in contrast the peraluminous high silica compositions of the te kinga suite were produced by melting at higher h2o contents reducing the stability of plagioclase and resulting in a melt in equilibrium with a plagioclase free eclogitic garnet amphibole residue residual plagioclase during generation of the deutgam suite resulted in lower al2o3 na2o sr ba and eu contents whereas residual garnet during generation of the te kinga suite resulted in depleted hree contents the mid cretaceous granitoids of the hohonu batholith were generated during a period of rapid tectonic transition from crustal thickening during collision to crustal thinning and core complex formation during extension

model for predicting displacement dependent lateral earth pressure a model for predicting displacement dependent lateral earth pressure was proposed based on an earth pressure displacement relationship commonly observed in practice the proposed model is a monot

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

petrogenesis and tectonic implications of neoproterozoic highly fractionated a type granites from mianning south china abstract the origin of neoproterozoic intrusions ca 860 750 ma along the western part of the yangtze craton has been the subject of debate in recent years with two competing models proposed the plume model argues for an extensional setting and emphasizes the role of a superplume in the rodinia breakup whereas the arc model argues for the presence of a subduction zone in the yangtze craton as a contribution to this animated dispute geochronologic and geochemical analyses have been carried out on the mianning granite which is the largest pluton 700 km2 in the northern kangdian rift of the western yangtze craton it is shown that the mianning granites were emplaced at ca 780 ma and display highly fractionated feature i e sio2 75 wt eu eu 0 03 0 50 enrichment of k rb th u zr hf y and rees depletion of nb ta ba sr p eu and ti they are metaluminous to strongly peraluminous a cnk 0 93 1 55 and contain abundant perthite and minor alkali riebeckite and sphene sharing the petrological and geochemical characters of a2 type granites positive nd t 2 97 5 24 and zircon hf t 9 2 12 1 values are consistent with a derivation by partial melting of a relatively young crust formed about 1000 900 ma given the general absence of a type granites in arc settings the mianning a type granites are suggestive of an anorogenic crustal extensional environment for the western yangtze craton during the neoproterozoic the data presented in this study are therefore consistent with an intracontinental rift model but are not sufficient to identify plume involvement in the neoproterozoic magmatism

petrogenesis of cretaceous adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china implications for geodynamics and cu au mineralization both adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china are associated with cretaceous cu au mineralization the shaxi quartz diorite porphyrites exhibit adakite like geochemical features such as light rare earth element lree enrichment heavy ree hree depletion high al2o3 mgo sr sr y and la yb values and low y and yb contents they have low end t values 3 46 to 6 28 and high 87sr 86sr i ratios 0 7051 0 7057 sensitive high resolution ion microprobe shrimp zircon analyses indicate a crystallization age of 136 3 ma for the adakitic rocks most volcanic rocks and the majority of monzonites and syenites in the luzong area are k rich or shoshonitic and were also produced during the cretaceous 140 125 ma they are enriched in lree and large ion lithophile elements and depleted in ti and nb and ba and exhibit relatively lower end t values ranging from 4 65 to 7 03 and relatively higher 87sr 86sr i ratios varying between 0 7057 and 0 7062 the shoshonitic and adakitic rocks in the luzong area have similar pb isotopic compositions 206pb 204pb 17 90 18 83 207pb 204pb 15 45 15 62 and 208pb 204pb 38 07 38 80 geological data from the luzong area suggest that the cretaceous igneous rocks are distributed along ne fault zones e g tanlu and yangtze river fault zones in eastern china and were likely formed in an extensional setting within the yangtze block the shaxi adakitic rocks were probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thickness of 50 km i e 1 5 gpa possibly leaving rutile bearing eclogitic residue the shoshonitic magmas in contrast originated mainly from an enriched mantle metasomatized by subducted oceanic sediments they underwent early high pressure 1 5 gpa fractional crystallization at the boundary between thickened 50 km lower crust and lithospheric mantle and late low pressure 1 5 gpa fractional crystallization in the shallow 50 km crust the adakitic and shoshonitic rocks appear to be linked to an intra continental extensional setting where partial melting of enriched mantle and delaminated lower crust was probably controlled by lithospheric thinning and upwelling of hot asthenosphere along ne fault zones e g tanlu and yangtze river fault zones in eastern china both the shoshonitic and adakitic magmas were fertile with respect to cu au mineralization

fractionation vs magma mixing in the wangrah suite a type granites lachlan fold belt australia experimental constraints abstract the wangrah suite granites lachlan fold belt australia reflect different stages of differentiation in the magmatic history of an a type plutonic suite in this study we use experimentally determined phase equilibria of four natural a type granitic compositions of the wangrah suite to constrain phases and phase compositions involved in fractionation processes each composition represents a distinct granite intrusion in the wangrah suite the intrusions are the danswell creek dcg wangrah wg eastwood eg and dunskeig granite dg ordered from most mafic to most felsic by increasing sio2 and decreasing feototal experimental investigation show that the initial water content in melts from dcg is between 2 3 wt h2o if the dcg is viewed as the parental magma for the wangrah suite then 1 fractionation of magnetite orthopyroxene and plagioclase 20 wt of the dcg composition leads to compositions similar to that of the eg 2 further fractionation of plagioclase quartz k feldspar and biotite 40 wt from the eg composition leads to the dg composition these fractionation steps can occur nearly isobarically and are confirmed by bulk rock ba sr rb and zr concentrations in contrast the generation of the most abundant wg composition cannot be explained by fractional crystallisation from the dcg at isobaric conditions because of the high k2o content of this granite magma mixing could be the process to explain the chemical distinctiveness of the wangrah granite from all the other granites of the wangrah suite

hydroacoustic investigation of submarine landslides at west mata volcano lau basin submarine landslides are an important process in volcano growth yet are rarely observed and poorly understood we show that landslides occur frequently in association with the eruption of west mata volcano in the ne lau basin these events are identifiable in hydroacoustic data recorded between 5 and 20 km from the volcano and may be recognized in spectrograms by the weak and strong powers at specific frequencies generated by multipathing of sound waves the summation of direct and surface reflected arrivals causes interference patterns in the spectrum that change with time as the landslide propagates observed frequencies are consistent with propagation down the volcano s north flank in an area known to have experienced mass wasting in the past these data allow us to estimate the distance traveled by west mata landslides and show that they travel at average speeds of 10 25 m s

passive earth pressures theories and tests the magnitude of the passive earth pressure that resists the movement of a structure is controlled by the amount the structure moves and the direction in which it moves strength and stiffness of the soil that resists its movement friction or adhesion on the interface between the structure and soil and shape of the structure the log spiral theory corrected for 3d effects provides an accurate means of computing ultimate passive pressures a hyperbolic expression together with estimated values of soil modulus and ultimate resistance provides a means of estimating the relationship between structural movement and passive resistance it is essential that the soil strength and stiffness used in making these estimates should be appropriate for the soil and the drainage conditions involved the results of an undrained passive pressure load test in stiff sandy silt and a drained passive pressure load test in well graded gravel are compared with passive pressures computed using the methods discussed reasonable agreement between the calculated and measured values shows that the log spiral theory corrected for 3d effects and the hyperbolic load deflection relationship provide an adequate means of estimating passive resistance for a wide range of conditions

amphibole out phase boundary in partially melted metabasalt its control over liquid fraction and composition and source permeability a number of experimental studies in recent years have demonstrated that partial melting of hydrated basalt at lower crustal to upper mantle pressures is capable of generating up to 40 high sio2 liquids closely comparable in many geochemical respects to tonalitic trondhjemitic granitoids ttg from these studies it is apparent that the initiation of melting coincides with the beginning of amphibole dehydration but that a broad reaction interval over which amphibole coexists with high sio2 liquids is defined by the wet basalt solidus on one side and the amphibole out phase boundary on the other the phase relations of an alkali rich tholeiitic metabasalt have been examined in the outer half of this region up to and beyond the amphibole out phase boundary results indicate that amphibole exerts a strong control over the amount and composition of coexisting liquid over this interval melt fraction increases slowly and gradually from 0 up to 20 30 between the wet basalt solidus and up to amphibole out but increases substantially from 30 to 50 across and immediately beyond it liquids are strongly to moderately peraluminous molar al2o3 cao na2o k2o a cnk 1 0 up to amphibole out neutral at the boundary a cnk 1 0 and increasingly metaluminous a cnk 1 0 beyond it up to amphibole out potassium is strongly partitioned into liquid relative to amphibole i e mineral melt kd 0 2 0 3 whereas titanium is strongly partitioned into liquid kd 2 0 6 0 physical and chemical criteria suggest that efficient melt segregation leading to ttg plutonism requires more than 20 30 batch melting of a garnet bearing basaltic protolith near or beyond the amphibole out phase boundary leaving dry residues of eclogite or garnet granulite and producing metaluminous liquids that are strongly depleted in heavy rare earth elements hrees and yttrium y lower degrees of melting may involve critical melting where melt is squeezed out of the residue by deformation of the crystalline matrix resulting in disequilibrium melt compositions

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

petrogenesis and time progressive evolution of the cenozoic continental volcanism in the biga peninsula nw anatolia turkey abstract the post collisional cenozoic magmatic activity in the biga peninsula nw anatolia started in the middle eocene 45 3 0 9 ma and lasted continuously until the late miocene 8 32 0 19 ma with minor punctuations producing widespread volcanoplutonic complexes these magmatic suites are characterized by calc alkaline high k calc alkaline shoshonitic mildly alkaline and alkaline series the middle eocene to middle miocene lavas have high lile lree lile hfse and 87sr 86sr i 0 7046 0 7087 and low nd i 1 2 to 6 4 values by contrast the late miocene lavas have the lowest 87sr 86sr i 0 7030 0 7033 and the highest nd i 2 6 to 6 7 values geochemical features of these rocks indicate two episodes of enrichment processes during the evolution of the eocene early miocene volcanism in the biga peninsula the first stage source enrichment metasomatism occurred within the continental lithospheric mantle as a result of the previous subduction event s and produced a heterogeneously enriched source the second stage crustal contamination resulted from interaction between the metasomatized mantle derived melts and those magmas derived from the sakarya crustal basement during their ascent to the surface slab breakoff induced asthenospheric upwelling caused the melting of metasomatized mantle lithosphere beneath the sakarya continent and produced the middle eocene calc alkaline lavas geochemical isotopic and age relationships suggest increasing amounts of crustal contamination and a decreasing subduction signature during the evolution of magmas from the eocene through the early miocene crustal input was peaked during the early miocene volcanism coinciding with the exhumation and rapid uplift of the kazdag metamorphic massif asthenospheric upwelling beneath the kazdag core complex contributed to the generation of hybrid magmas formed from mixing of mantle and crustal melts during this stage the middle miocene 15 2 ma mildly alkaline rocks show less pronounced enrichment in lile and lree and display intermediate major and trace element compositions between the early miocene and late miocene lavas the cenozoic volcanism in biga peninsula waned briefly during 15 11 ma and was subsequently rejuvenated late miocene 11 0 0 4 8 32 0 19 ma producing mainly oib type alkaline lavas advanced extensional tectonics throughout nw anatolia in the late miocene led to upwelling of the asthenospheric mantle and its decompressional melting that collectively resulted in the eruption of short lived episodes of mainly oib type alkaline lavas this tectonomagmatic evolution of the cenozoic continental volcanism in western anatolia presents a well documented case study of an idealized post collisional magmatism in most orogenic belts around the world

nd isotope evidence for crust mantle interaction in the generation of a type granitoid suites in labrador canada early proterozoic a type granite suites in labrador northeastern canada have initial nd isotopic compositions that lie between those of a depleted mantle reservoir and the local basement rocks one of these a type granite suites consists of a linear array of discrete plutons that crosses the boundary between an archean craton and an adjoining early proterozoic crustal block the nd of these granites at formation t 1720 ma changes from 8 to 4 across this boundary reflecting changes in the nature and antiquity of the continental crust however in both domains the granites cannot be derived entirely by anatexis of the local basement rocks and apparently require significant amounts of juvenile mantle derived material a type granites have been widely interpreted as anatectic derivatives of lower crustal rocks that were depleted by previous melt extraction the nd isotopic data suggest that these labrador examples were instead mixtures of mantle derived magmas and overlying lower crustal rocks and that new material may have been the volumetrically dominant component 50 90 in most cases as an alternative to the prevalent residual source model it is proposed that the distinctive geochemical characteristics of these a type granites are a function of the high liquidus temperatures and primitive mg rich character of subcrustal magma fluxes in post orogenic and anorogenic environments where such magmas are emplaced into stabilized continental crust further nd isotope studies of other a type granite suites are required to ascertain if models invoking crust mantle interaction are more widely applicable

k ar ages of granitoids unravel the stages of neo tethyan convergence in the eastern pontides and central anatolia turkey k ar dating of mineral separates extracted from various granitoid rock units of the eastern pontides and central anatolia turkey has provided some new insights unravelling various stages of the neo tethyan convergence system which evolved with northward subduction between the eurasian plate ep to the north and the tauride anatolide platform tap to the south along the izmir ankara erzincan suture iaes zone arc related granitoid rocks are only encountered in the eastern pontides and yield k ar cooling ages of both early cretaceous 138 5 2 2 ma early arc and late cretaceous ranging from 75 7 0 0 to 66 5 1 5 ma mature arc respectively the multi sourced granitoids of the eastern pontides with a predominant mantle component and k ar ages between 40 and 50 ma are considered to be a part of post collisional slab break off magmatism accompanied by tectonic denudation of pre late cretaceous granitoid rocks following juxtaposition of the ep and the tap around 55 50 ma in the eastern pontides the k ar cooling ages of collision related s i and a type granitoids in central anatolia reflect good synchronism between 80 and 65 ma suggesting a coeval genesis in a unique geodynamic setting but with derivation from various sources namely purely crustal purely mantle and or of mixed origin this sort of simultaneous generation model for these s i a type intrusives seems to be consistent with a post collisional lithospheric detachment related geodynamic setting i type granodioritic to tonalitic intrusives with k ar cooling ages ranging from 40 to 48 ma in east central anatolia are interpreted to have been derived from a post collisional within plate extension related geodynamic setting following the amalgamation of the ep and the tap in east central anatolia

deformation mechanisms and evolution of a pile reinforced landslide under long term reservoir operation abstract stabilizing piles are widely used for reinforcing landslides in the three gorges reservoir area china due to reservoir operations long term water level fluctuations wlfs may cause instability or failure of the reservoir landslide and piles system rlps this study experimentally investigated the deformation characteristics and mechanisms of the rlps under long term wlfs the results showed that long term wlfs led to loading and unloading cycles and consequently a weakening of the slope stability where retrogressive failure and system instability were observed retrogressive failure at the slope toe was caused by topographical variation and physical and mechanical deterioration which may be a result of the long term wlfs system instability was accompanied by a stress release process above the new slip surface and was determined to be dependent on the geological structure of the rlps based on this investigation the evolution model of the pile reinforced landslide under long term wlfs was proposed even though the rlps was adversely affected by the long term wlfs it maintained a relatively steady state due to the reinforcement of the piles effective pile installation changed the development of the reservoir landslides and prevented the entire slip surface from reaching a critical state thus a catastrophic consequence was avoided except for the local failure through physical modeling this study experimentally provided a deeper understanding of the deformation mechanisms and evolution of the rlps influenced by the long term wlfs

the role of fe ti oxide crystallization in the formation of a type granitoids with implications for the daly gap an example from the permian baima igneous complex sw china abstract the baima igneous complex bic is a member of the permian emeishan large igneous province sw china and is composed of a layered gabbroic unit and an isotropic syenitic unit the gabbroic unit consists of four distinct zones 1 lower cumulate zone 2 massive fe ti v oxide ore zone 3 olivine gabbro zone and 4 upper gabbro zone shrimp zircon u pb dating results yield an age of 261 2 ma for the gabbroic unit contemporaneous with the spatially associated syenitic unit the gabbroic rocks show slightly lree enriched patterns with la yb n values between 1 6 and 12 1 and positive eu anomalies eu eu 1 1 3 6 in contrast the syenites display stronger enrichments of lree la ybn 6 8 51 3 and negative eu anomalies eu eu 0 3 1 1 rocks of the syenitic unit are chemically similar to the ferroan alkalic a type granitoids k2o na2o 0 58 0 80 feot feot mgo 0 80 0 91 and have a within plate geochemical signature both units have similar trace element ratios zr nb th u ni co cu ni hf ta and zn ga resembling an ocean island basalt source the end t values for the gabbroic unit end t 1 6 4 2 and syenitic unit end t 2 5 3 2 are within the range of the high ti emeishan flood basalts the geochemical and geochronological data indicate that the gabbroic and syenitic units are comagmatic and cogenetic geochemical modeling suggests that the two units originated by fractional crystallization of a common parental magma that resembles the high ti emeishan flood basalts the formation of the two units by fractional crystallization was likely responsible for the enrichment of fe ti v oxide minerals in the gabbroic unit and thus the development of the daly gap the results of this study indicate that silica saturated peralkaline a type granitoids can be formed by fractionation of mantle derived mafic magmas

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

tectonic evolution of the orogenic belt in the region located between kerman and neyriz abstract tectonic evolution of the orogenic belt in the region located between kerman and neyriz is explored within the context of two ne dipping neotethyan subduction zones the northern subduction zone was responsible for formation of the mesozoic sanandaj sirjan magmatic arc and the late cretaceous shahr babak baft ensimatic back arc extensional basin the southern subduction zone was responsible for formation of the reverse primitive neyriz island arc the central iranian volcanic belt and its line of porphyry copper deposits as well as the rafsanjan back arc extensional basin proto rafsanjan depression due to the collision of the neyriz island arc with the sanandaj sirjan active continental margin the shahr babak baft back arc basin was tectonically inverted into the shahr babak baft ophiolite belt finally the continental collision between the arabian and the central iranian plates took place during the neogene this led to the tectonic inversion of the rafsanjan ensialic basin into the rafsanjan retro arc basin the present rafsanjan depression and emplacement of the syncollision to late or post orogenic granitoid rocks felsic mass in the rafsanjan region

lead isotope data from the sar cheshmeh porphyry copper deposit iran lead isotope compositions of nine sulfide concentrates from ore samples from the sar cheshmeh deposit are reported they range from virtually unaltered granodiorite through varying degrees of potassic alteration to ores showing strong phyllic alteration sericite veins the samples without strong phyllic alteration have fairly uniform lead isotope compositions around 206pb 204pb 18 6 207pb 204pb 15 6 and 208pb 204pb 38 7 two samples with sericite veins have markedly more radiogenic lead it is concluded that the fluid responsible for the potassic alteration and the associated mineralization was essentially magmatic whereas convecting meteoric water from the country rock acted as a mineralizing solution during phyllic alteration in the context of the plumbotectonics model the deposit has a typical orogen signature intermediate between primitive and mature island arc settings

late orogenic post orogenic and anorogenic granites distinction by major element and trace element chemistry and possible origins granites classified into four categories based solely on tectonics of occurrence and associated rock types also have compositional characteristics that are consistent within groups and different am

on the propagation of acoustic gravity waves under elastic ice sheets the propagation of wave disturbances in water of varying depth bounded above by ice sheets is discussed accounting for gravity compressibility and elasticity effects considering the more realistic scenario of elastic ice sheets reveals a continuous spectrum of acoustic gravity modes that propagate even below the cutoff frequency of the rigid surface solution where surface gravity waves cannot exist the balance between gravitational forces and oscillations in the ice sheet defines a new dimensionless quantity mathfrak ka when the ice sheet is relatively thin and the prescribed frequency is relatively low mathfrak ka ll 1 the free surface bottom pressure solution is retrieved in full however thicker ice sheets or propagation of relatively higher frequency modes mathfrak ka gg 1 alter the solution fundamentally which is reflected in an amplified asymmetric signature and different characteristics of the eigenvalues such that the bottom pressure is amplified when acoustic gravity waves are transmitted to shallower waters to analyse these scenarios an analytical solution and a depth integrated equation are derived for the cases of constant and varying depths respectively together these are capable of modelling realistic ocean geometries and an inhomogeneous distribution of ice sheets

the geology of kimberlite pipes of the ekati property northwest territories canada abstract this paper reviews key characteristics of kimberlites on the ekati property nwt canada to date 150 kimberlites have been discovered on the property five of which are mined for diamonds the kimberlites intrude archean basement of the central slave craton numerous proterozoic diabase dykes intrude the area the precambrian rocks are overlain by quaternary glacial sediments no phanerozoic rocks are present however mudstone xenoliths and disaggregated sediment within the kimberlites indicate that late cretaceous and tertiary cover likely

constraints on arabian plate motion and extensional history of the red sea analysis of the geologic and geophysical data from the western and northern margin of the arabian plate combined with data from the red sea gulf of aden leads to an interpretation of arabian plate motion that supports an episodic extensional history in the red sea and gulf of aden phase 1 extension began in medial to late eocene and was caused by the nw propagation of the reoriented central indian ridge spreading center it stretched and thinned continental crust along numerous wrench and normal faults that reactivated preexisting structures first phase extension stopped when the arabian plate terminally sutured to eurasia in the medial miocene and halted northward movement of arabia relative to africa the combined african arabian plates moved north more slowly constricting and thickening continental crust in the bitlis zagros sutures while the red sea remained technically quiescent and accumulated salt by the early pliocene continued northward movement was accommodated by lateral extrusion of large continental wedges north of the bitlis zagros sutures this allowed arabia to move northward faster than africa and reopen the red sea where phase 2 extension was expressed by seafloor spreading extension within the red sea gulf of aden rift system has been controlled by the interactions and effects of two factors 1 convergent processes between the north margin of the arabian plate and the eurasian plate to the north and 2 northwest propagation of extension associated with the medial eocene reorganization of the central indian spreading center

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

a new tectonic scenario for the sanandaj sirjan zone iran abstract recent geochemical studies of volcanic rocks forming part of the ophiolites within the zagros and naien baft orogen indicate that most of them were developed as supra subduction ophiolites in intra oceanic island arc environments intra oceanic island arcs and ophiolites now forming the naien baft zone were emplaced southwestward onto the northeastern margin of the south sanandaj sirjan zone while those now in the high zagros were emplaced southwestward onto the northern margin of arabia thereafter subduction continued on opposite sides of the remnant oceans the floor of neo tethys ocean was subducted at a low angle beneath the entire sanandaj sirjan zone and the floor of the naien baft ocean was subducted beneath the central iranian micro continent the naien baft ocean extended into north west iran only temporarily this failed ocean arm between the urumieh dokhtar magmatic assemblage and the main zagros thrust was filled by thick upper triassic upper jurassic sediments the naien baft ocean finally closed in the paleocene and neo tethys closed in the early to middle eocene after arabia was sutured to iran the urumieh dokhtar magmatic assemblage recorded slab break off in the middle eocene

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

hydro acoustic precursors of gravity waves generated by surface pressure disturbances localised in space and time we consider the mechanics of coupled underwater acoustic and surface gravity waves generated by surface pressure disturbances in a slightly compressible fluid we show that pressure changes on the ocean surface localised in space and time can induce appreciable underwater compression waves which are precursors of the surface gravity waves although the physical properties of acoustic gravity waves have already been discussed in the literature such dynamics was not investigated in previous studies we derive new results for the underwater compression wave field and discuss the dynamics of its generation and propagation this work could lead to the design of innovative alert systems for coastal flooding management

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

reduced rapakivi type granites the tholeiite connection reduced rapakivi type granites are the most iron enriched and reduced i e least oxidized of the anorogenic granite association the low oxygen fugacity and chemical composition of these granites severely limit their sources in this paper we argue that reduced rapakivi type granites and their eruptive equivalents high potassium fayalite rhyolites are derived from mafic sources because tholeiitic magmas and their derivatives have the required low oxygen fugacity reduced rapakivi type granites are produced either by extreme differentiation of basaltic melts or by partial melting of underplated basalts and their differentiated equivalents they form in extensional environments where the asthenosphere is present at shallow depths we envision three stages in the origin of these rocks 1 tholeiitic melts are emplaced at the base of the crust 2 continued introduction of heat partially remelts these tholeiitic rocks and 3 the hot dry melts so produced migrate into the middle crust to produce rapakivi batholiths or erupt as rhyolites partial melting of felsic continental crust may accompany the intrusion of rapakivi type magmas thereby producing the other metaluminous and peraluminous granite compositions of the anorogenic suite

arabia eurasia collision and the forcing of mid cenozoic global cooling the end of the eocene greenhouse world was the most dramatic phase in the long term cooling trend of the cenozoic era here we show that the arabia eurasia collision and the closure of the tethys ocean gateway began in the late eocene at 35 ma up to 25 million years earlier than in many reconstructions we suggest that global cooling was forced by processes associated with the initial collision that reduced atmospheric co2 these are 1 waning volcanism across southwest asia 2 increased organic carbon storage in paratethyan basins e g black sea and south caspian 3 increased silicate weathering in the collision zone and 4 a shift towards modern patterns of ocean currents associated with increased vigour in circulation and organic productivity

the triassic cobquecura pluton central chile an example of a fayalite bearing a type intrusive massif at a continental margin abstract the late triassic cobquecura pluton is a small epizonal intrusive body that was emplaced into the paleozoic basement at the western side of the cordillera de la costa near to the town of cobquecura 35 57 36 12 s central chile the pluton displays a wide spectrum of compositions that include gabbro and fayalite granite and less abundant hybrid rocks sio2 content ranges from 48 to 76 wt with a compositional gap between 57 and 63 wt sio2 sio2 poor rocks have mg fe minerals olivine fa33 34 diopside augite mg 56 91 mg mg mg fe2 100 and pargasite mg 4 8 which with progressive differentiation become fe rich olivine fa89 98 hedenbergite ferroaugite mg 10 43 and ferroedenite mg 8 29 similar k ar isotopic ages mingling structures and coherent arrays in harker diagrams as well as mineral compositions show that the sio2 poor and sio2 rich rocks are comagmatic the fe rich mineralogy and ga content of the cobquecura pluton point to an anorogenic a type magmatism the compositional similarities as well as the bimodal character of the magmatism of cobquecura and other upper triassic granitoids and lavas north of 30 s at the chilean continental margin indicate a common origin of the magmatism with anorogenic signature and coeval processes along the southwestern margin of gondwana in the triassic

late cenozoic reorganization of the arabia eurasia collision and the comparison of short term and long term deformation rates the arabia eurasia collision deforms an area of 3 000 000 km2 of continental crust making it one of the largest regions of convergent deformation on earth there are now estimates for the active slip rates total convergence and timing of collision related deformation of regions from western turkey to eastern iran this paper shows that extrapolating the present day slip rates of many active fault systems for 3 7 million years accounts for their total displacement this result means that the present kinematics of the arabia eurasia collision are unlikely be the same as at its start which was probably in the early miocene 16 23 ma or earlier in some but not all active fault systems short term 10 year and long term 5 million year average deformation rates are consistent there is little active thickening across the turkish iranian plateau and possibly the interior of the greater caucasus these are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening and where there are structural and or stratigraphic data for pre late miocene deformation we suggest that once thick crust up to 60 km built up in the turkish iranian plateau and the greater caucasus convergence took place more easily by crustal shortening in less elevated regions such as the zagros simple folded zone the south caspian region and foothills of the greater caucasus or in other ways such as westward transport of turkey between the north and east anatolian faults the time and duration of this changeover are not known for certain and are likely be diachronous although deformation started or intensified in many of the currently active fault systems at 5 2 ma

the association of mafic ultramafic intrusions and a type magmatism in the tian shan and altay orogens nw china implications for geodynamic evolution and potential for the discovery of new ore deposits abstract the nw china region is characterised by tectonic and lithostratigraphic domains such as the tian shan and altay orogens the tarim junggar and turpan basins the tian shan and altay orogens are part of the central asian orogenic belt the nw china region was affected by a series of thermal events that occurred between the silurian and the triassic which resulted in the emplacement of numerous granitic plutons and mafic ultramafic intrusions a number of these granitic plutons are of a type affiliation which on the basis of the positive end values are likely to have been derived from mantle sources in addition at least two large igneous provinces lips can be recognised in nw china namely the 345 325 ma tian shan lip and the ca 270 280 ma tarim lip age and field data suggest a spatial and temporal relationship between the mafic ultramafic intrusions and a type granites within the lips in this paper we discuss mafic ultramafic intrusions that host magmatic ni cu sulphide deposits kalatongke in the altay huangshan and poyi poshi in the eastern tian shan these intrusions are typically zoned characterised by an envelope of early gabbroic rocks that enclose later ultramafic units these zoned mafic ultramafic intrusions have some features that are comparable with alaskan type complexes taking into consideration the spatial temporal relationship of the mafic mafic ultramafic rocks and a type granites we suggest that these magmatic events occurred during an extensional regime possibly related to a mantle superplume event that affected much of central asia during the permian of which the siberian traps and the emeishan continental flood basalts of sw china are part if the a type felsic magmatism took place during a superplume event we also suggest that these rocks may be conducive to host iron oxide copper gold iocg style mineralisation we conclude with a model that attempts to explain the relationship between the zoned mafic ultramafic intrusions and mantle plume activity in nw china during the permian

intracontinental extensional magmatism with a subduction fingerprint the late carboniferous halle volcanic complex germany the halle volcanic complex hvc is part of the transtensional intracontinental saale basin which formed on the mid german crystalline rise located at the southern margin of the late carboniferous early permian volcanic province of central europe magmatic activity ranged from early trachybasalts trachyandesites and trachydacites followed by calc alkaline mildly peraluminous low si rhyolites the latter of which had intruded at a very shallow crustal level two groups of geochemically heterogeneous and isotopically distinct mafic intermediate rocks have to be distinguished which originated from enriched mantle lower crustal sources and experienced crustal contamination to various extents these rocks preceded the emplacement of rhyolites that are remarkably uniform in major and trace element chemistry as well as nd isotope composition distinctly negative end t 300 ma 6 7 to 7 0 of the rhyolites implies significant involvement of crustal material the pb isotopic composition of k feldspar and trace element content of the rhyolites are compatible with remelting of saxothuringian rather than rhenohercynian crustal domains of the variscan orogen slightly differing ree abundances in the rhyolites are attributed to an inhomogeneous distribution of accessory minerals in conflict with their generation in an extensional environment the trace element signature of the hvc rocks indicates a magmatic arc or collisional setting rather than an intracontinental within plate setting the composition of rhyolites from extensional settings at halle and the adjacent northeast german basin demonstrates that trace element composition and geodynamic environment may not be correlated furthermore the geochemistry of these rocks implies that the same type of magmatism may take entirely different chemical expressions in dependence of the structural and chemical composition of the underlying lithospheric block which might be used to map hidden destroyed terrain boundaries in ancient orogens

cretaceous tertiary convergence and continental collision sanandaj sirjan zone western iran abstract the sanandaj sirjan zone contains the metamorphic core of the zagros continental collision zone in western iran the zone has been subdivided into the following from southwest to northeast an outer belt of imbricate thrust slices radiolarite bisotun ophiolite and marginal sub zones which consist of mesozoic deep marine sediments shallow marine carbonates oceanic crust and volcanic arc respectively and an inner complexly deformed sub zone late palaeozoic mesozoic passive margin succession rifting and sea floor spreading of tethys occurred in the permian to triassic but in the sanandaj sirjan zone extension related successions are mainly of late triassic age subduction of tethyan sea floor in the late jurassic to cretaceous produced deformation metamorphism and unconformities in the marginal and complexly deformed sub zones deformation climaxed in the late cretaceous when a major southwest vergent fold belt formed associated with greenschist facies metamorphism and post dated by abundant palaeogene granitic plutons in the southwest of the zone a late cretaceous island arc passive margin collision occurred with ophiolite emplacement onto the northern arabian margin similar to that in oman final closure of tethys was not completed until the miocene when central iran collided with the northeast arabian margin

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

petrogenesis of the paleoproterozoic rapakivi a type granites of the archean carajas metallogenic province brazil three paleoproterozoic a type rapakivi granite suites jamon serra dos carajas and velho guilherme are found in the carajas metallogenic province eastern amazonian craton liquidus temperatures in the 900 870 c range characterize the jamon suite those for serra dos carajas and velho guilherme are somewhat lower pressures of emplacement decrease from jamon 3 2 0 7 kbar through serra dos carajas 2 0 1 0 kbar to velho guilherme 1 0 0 5 kbar oxidizing conditions nno 0 5 characterized the crystallization of the jamon magma the velho guilherme magmas were reducing marginally below fmq and the serra dos carajas magmas were intermediate between the two in this respect the three granite suites have archean tdm model ages and strongly negative nd values 12 to 8 at 1880 ma and they were derived from archean crust the jamon granite suite may have been derived from a quartz dioritic source and the velho guilherme granites from k feldspar bearing granitoid rocks with some sedimentary input the serra dos carajas granites either had a somewhat more mafic source than velho guilherme or were derived by a larger degree of melting underplating of mafic magma was probably the heat source for the melting the petrological and geochemical characteristics of the carajas granite suites imply considerable compositional variation in the archean of the eastern amazonian craton the oxidized jamon suite granites are similar to the mesoproterozoic magnetite series granites of laurentia and they were derived from archean igneous sources that were more oxidized than the sources of the fennoscandian rapakivi granites the serra dos carajas and velho guilherme granites approach the classic reduced rapakivi series of fennoscandia and laurentia no counterparts of the mesoproterozoic two mica granites of laurentia have been found however following the model of hoffman hoffman p 1989 speculations on laurentia s first gigayear 2 0 to 1 0 ga geology 17 135 138 the origin of the 1 88 ga carajas granites is related to a mantle superswell beneath the trans amazonian supercontinent this caused breakup of the continent and was associated with magmatic underplating and resultant crustal melting and generation of a type granite magmas the paleoproterozoic continent that included the archean and trans amazonian domains of the amazonian craton was assembled at 2 0 ga its disruption was initiated at 1 88 ga at least 200 ma earlier than in laurentia and fennoscandia the carajas granites were related to the breakup of the supercontinent not to subduction processes

modeling of the hydroacoustic signal and tsunami wave generated by seafloor motion including a porous seabed 1 within the framework of a 2 d compressible tsunami generation model with a flat porous seabed acoustic waves are generated and travel outward from the source area the effects of the porous seabed during tsunami generation and propagation processes include wave amplitude attenuation and low pass filtering of both the hydroacoustic signal and tsunami wave the period of the acoustic wave generated by the seafloor motion depends on water depth over the source area and is given by four times the period of time required for sound to travel from the seabed to the surface these waves carry information about seafloor motion the semianalytical solution of the 2 d compressible water layer model overlying a porous seabed is presented and discussed furthermore to include the effects generated by the coupling between compressible porous sedimentary and water layers a simplified two layer model with the sediment modeled as a compressible viscous fluid is presented

k ar age whole rock and isotope geochemistry of a type granitoids in the divrigi sivas region eastern central anatolia turkey abstract the bimodal a type dumluca and murmana granitoids consist of felsic monzonitic syenitic and mafic gabbroic dioritic and monzogabbroic monzodioritic rocks which were intruded into the cenomanian turonian supra subduction zone type divrigi ophiolitic melange new hornblende and biotite k ar dates yield cooling ages ranging from 72 to 77 ma and from 68 to 77 ma for the felsic and mafic rocks respectively in the dumluca and murmana granitoids felsic and mafic rocks of these intrusions have a metaluminous high k alkaline composition however highly evolved members of the felsic rocks are peraluminous in character trace element geochemistry data indicate that mafic and felsic rocks have their own geochemical characteristics which show different sources the combined evidence of the trace element radiogenic and stable isotope geochemistry from the dumluca and murmana granitoids suggest that the mafic rocks were derived exclusively from an enriched mantle mafic magma em ii but the felsic rocks were derived from a hybrid felsic magma the hybrid felsic magma was generated by the mixing of the mantle derived mafic with another crustal derived silicic melt the composition of some mafic rocks from murmana granitoid suite is thought to be derived from an enriched mantle source that may have been metasomatized by earlier subduction derived fluids thus carrying the subduction signature in the source material the local and regional geology suggest an early late cretaceous post collisional extension related geodynamic setting following the collision between the tauride anatolide platform and an oceanic island arc comprising the supra subduction zone type central anatolian ophiolite