identifying granite sources by shrimp u pb zircon geochronology an application to the lachlan foldbelt the potential genetic link between granites and their host sediments can be assessed using zircon age inheritance patterns in the lachlan fold belt southeastern australia granites and associated high grade metasedimentary rocks intrude low grade ordovician country rock this relationship is well exposed in the tallangatta region northeast victoria part of the wagga omeo metamorphic complex in this region granites two i types and two s types have intruded during the mid late silurian between approximately 410 430 ma based on the ages of magmatic zircons the age spectra for inherited zircons from the granites have been compared with those of detrital zircons from the enclosing low and high grade metasediments in broad terms both for detrital zircons in all four sediments and for inherited zircons in three of the four granites the dominant ages are early paleozoic and late precambrian with sporadic older precambrian ages extending up to 3 5 ga the ages of the youngest detrital zircons from the low grade lockhart and talgarno terranes limit the time of sedimentation to ca 466 ma or younger the youngest detrital zircons from two samples of the high grade gundowring terrane are 473 ma making these sediments ordovician or younger not cambrian as originally suggested however the individual age spectra for the four selected metasediments are not well matched when closely examined the age spectra of the inherited zircons in the granites also do not adequately match those in any of the metasediments thus the metasediments might not be representative of the actual source rocks of the granites while the exact source of the granites cannot be identified from the analysed samples the existence of a large population of ca 495 ma inherited zircon grains in the s type granites requires that the granite source contains a significant proportion of cambrian or younger material this does not preclude the existence of a precambrian basement to the lachlan fold belt but indicates that at the level of s type magma generation a cambrian and or younger protolith is required

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

volcanic plutonic parity and the differentiation of the continental crust the continental crust is central to the biological and geological history of earth however crustal heterogeneity has prevented a thorough geochemical comparison of its primary igneous building blocks volcanic and plutonic rocks and the processes by which they differentiate to felsic compositions our analysis of a comprehensive global data set of volcanic and plutonic whole rock geochemistry shows that differentiation trends from primitive basaltic to felsic compositions for volcanic versus plutonic samples are generally indistinguishable in subduction zone settings but are divergent in continental rifts offsets in major and trace element differentiation patterns in rift settings suggest higher water content in plutonic magmas and reduced eruptibility of hydrous silicate magmas relative to dry rift volcanics in both tectonic settings our results indicate that fractional crystallization rather than crustal melting is predominantly responsible for the production of intermediate and felsic magmas emphasizing the role of mafic cumulates as a residue of crustal differentiation a global geochemical data set of volcanic and plutonic rocks indicates that differentiation trends from primitive basaltic to felsic compositions for volcanic versus plutonic samples are generally indistinguishable in subduction zone settings but are divergent in continental rifts brenhin keller and co authors present a global geochemical dataset of the two fundamental building blocks of the continental crust volcanic externally erupted and plutonic internally solidified rocks their results indicate that differentiation trends from primitive basaltic to felsic compositions for volcanic versus plutonic samples are generally indistinguishable in subduction zone settings but divergent in continental rifts offsets in major and trace element differentiation patterns in rift settings suggest higher water content in plutonic magmas and reduced eruptibility of hydrous silicate magmas relative to dry rift volcanics this work indicates that in both tectonic settings fractional crystallization rather than crustal melting is predominantly responsible for the production of intermediate and felsic magmas

an isotopic mixing model for the origin of granitic rocks in southeastern australia a simple mixing process was a significant element in the genesis of many southeastern australian granitic rocks major and trace element abundances are near linearly correlated nd and sr initial isotopic compositions define a simple hyperbolic trend and many initial 87sr 86sr ratios are a regular function of rb sr ratios geological arguments and regression of geochemical variation diagrams place limits on the nature of the end members the high si end member is meta sedimentary derived magma comparable in composition to the cooma granodiorite the one pluton in the region surrounded by and clearly derived from regional metamorphic rocks the low si end member is basaltic material with similarities to rare gabbros also found in the area isotope dilution calculations based upon initial sr and nd isotopic compositions deduced for the end members yield realistic hypothetical sr and nd concentrations for the end members in a demonstration of the internal consistency of the model all of the granitic rocks from hornblende tonalites to cordierite granodiorites are a single broad family products of variable mixing between distinct batches of basaltic material and a uniform partial melt of the regional basement

fractional crystallization of mantle derived melts as a mechanism for some i type granite petrogenesis an example from lachlan fold belt australia the mt buller igneous suite in the southeastern lachlan fold belt encompasses a large variety of rock types from gabbros through diorites to granites mafic rocks and enclaves have primitive mantle like initial 87 sr 86 sr values 0 7037 0 7045 and nd values 5 6 to 4 1 the granites do not show distinctively more radiogenic initial 87 sr 86 sr values suggesting they are derived from the same parent as the gabbros most of the mt buller rocks do not show a positive correlation between silica and initial 87 sr 86 sr or between silica and 143 nd 144 nd values indicating that neither crustal contamination nor mixing between mantle and crustal derived melts has been important and that these rock types are likely to have formed by fractional crystallization from a common mantle derived parent some scatter in compatible trace elements particularly in granites and diorites may be explained by mixing geochemical modelling confirms a comagmatic origin of the suite magma generation probably took place in the subduction modified upper mantle this mechanism may play an important role in i type granite petrogenesis in particular tectonic settings such as during an efficient slab roll back or sinking of oceanic crust in divergent subduction conditions

the identification and significance of pure sediment derived granites the characterization of the geochemical reservoirs of the earth s continental crust including the determination of representative upper and lower crustal compositions underpins our understanding of crustal evolution the classic i and s type granite classification has often been invoked to distinguish between melts derived from igneous protoliths and those derived from the melting of a sedimentary source recent geochemical studies suggest that most granites even those cited as typical examples of s type show evidence for a mixture of mantle and upper crustal sources thereby implying that granite formation is evidence for overall crustal growth we have examined the source of leucogranite bodies in one of the world s youngest collisional orogens using novel zircon techniques that can resolve the presence of even minor mantle contributions 232 zircons from 12 granites from the bhutan himalaya were analysed by in situ techniques for o hf and u pb isotopic signatures in combination with data from the granite host rocks our data show that the himalayan leucogranites were derived solely from metamorphosed crustal sediments and do not record any mantle contribution this finding is consistent with the time lag between crustal thickening and widespread crustal melting and the heat producing capacities of the pelitic source rocks we conclude that himalayan leucogranites provide a more suitable type locality for s type granites than the lachlan area in south east australia where the term was first defined the himalayan leucogranites therefore provide evidence that syn orogenic melting during collisional events does not necessarily result in crustal growth importantly crustal growth models should not always assume that crustal growth is achieved during collisional orogenesis

geochemistry and origin of early proterozoic dongargarh rapakivi granite complex central india an example for magma mixing and differentiation abstract early proterozoic dongargarh granite complex of central india intruding the tonalitic to granodioritic amgaon gneisses and the nandgaon group bimodal volcanic suite comprises three different textural and compositional types viz porphyritic granodiorite pg coarse equigranular granite eg and microgranite mg synplutonic mafic dykes are common in the granite complex the pg is characterised by rapakivi texture and the eg is the dominant facies and exhibits sporadically developed rapakivi texture microgranular enclaves are common in the eg while they are rare in pg major and trace element geochemistry of pg shows marked i type and some occasional a type granite characters unusual for a rapakivi granite while the eg shows a type granite signatures the field petrographic chemical and isotopic data of these granites suggest their derivation by mixing of mantle derived basic magma with a crustal derived partly crystalline granitic magma episodic mafic magma underplating caused the anatexis of the archaean lower continental crust in a continental margin tectonic setting resulting first in the formation of the i type granodiorite followed by a type granite the i type granodiorite is mixed with the basic magma synplutonic dykes while the eg is formed by mingling of a type granite magma and the intruding basic magma

geostrophic versus friction dominated storm flow palaeocurrent evidence from the late permian brotherton formation england the late permian brotherton formation of northeastern england is a 0 75 m thick carbonate sequence which exhibits abundant erosively amalgamated hummocky cross stratification gutter casts and shallow scour fills suggesting deposition in a storm dominated platformal shelf setting the outcrop ca 15 m thick is divisible into three facies associations a basal transgressive interval 4 5 m thick facies association a which passes upwards into a thinly bedded argillaceous condensed section 1 m thick facies association b which in turn rapidly grades upwards into a 8 10 m thick regressive highstand succession of hummocky cross stratified amalgamated scour fills facies association c the dominance of hummocky cross stratification in all facies associations would suggest that post storm deposition and fairweather reworking was largely under oscillatory currents however the erosional palaeocurrent data indicate that facies associations a and b were deposited following combined oscillatory and geostrophically balanced shore parallel flows in contrast facies association c was deposited by infilling the scours of friction dominated offshore directed and downwelling jet like flows combined with oscillatory wave currents the dominance of geostrophic or friction dominated flows in the study area is interpreted to be controlled by relative sea level changes during transgressive conditions increasing accommodation permitted rotation of the downwelling pressure driven currents in the regressive phase particularly in the accommodation limited late highstand bottom friction was important in inhibiting flow rotation it is suggested that the paucity of evidence for geostrophic flows in the ancient record may in part be attributed to the palaeocurrent indicators in sand grade substrates being restricted to thin transgressive intervals or surfaces whilst in the volumetrically more important regressive deposits palaeocurrent data are largely contained within facies from the friction dominated zone

on the origins of granites granites make up a large part of the continental crust new data reveal their complex and diverse formation history calling for a revision of the geological histories of many granites

constraints from zircon u pb ages o and hf isotopic compositions on the origin of neoproterozoic peraluminous granitoids from the jiangnan fold belt south china zircon textures and micro chemical compositions precisely record the origin and petrogenesis of granitoids which are crucial for evaluating crustal growth and reworking thermal and geodynamic evolution zircons in peraluminous granitoids from the three largest 820 ma complexes guibei yueyang and jiuling in the jiangnan fold belt in south china are used to constrain their sources and petrogenetic processes zircons in the guibei granitoids have complex internal structures nearly all magmatic and inherited zircons have similar ehf 6 8 to 5 6 and 18o values 8 8 11 6 and dominantly lie between ehf evolution vectors for a crust created between 1 7 and 2 1 ga suggesting that the guibei granitoids were produced by partial melting of recycled heterogeneous supracrustal material however the yueyang granitoids contain zircons with high ehf 0 5 to 9 7 and relatively low 18o values 5 9 8 4 and two stage model ages of 1 1 1 8 ga and thus may have been formed by melting of mafic rocks from the lower crust the jiuling granitoids and their enclaves contain more complex zircons with more variable ehf 7 2 to 9 7 and 18o values 7 0 10 6 and lie along the mixing trend between the above proposed infracrustal and supracrustal granitoids therefore the neoproterozoic peraluminous granitoids in the jiangnan fold belt were produced by melting and mixing of continental crust compared with extremely low 4 and negative 18o values of neoproterozoic igneous zircons formed in its northern active continental margin the high 18o peraluminous granitoids in the southeastern yangtze block are considered to have been formed by melting of hydrothermally unaltered continental crust triggered by asthenosphere upwelling in the nanhua back arc basin

structural setting and geochemistry of archaean i type granites in the bardoc coolgardie area of the norseman wiluna belt western australia abstract regional structures in the bardoc coolgardie area of the archaean norseman wiluna greenstone belt in western australia developed during early large scale thrusting followed by a transpressional regime characterized by enewsw shortening and large scale sinistral strike slip faults structural relationships between granites and greenstone successions indicate emplacement of granitic rocks throughout this deformation history emplacement mechanisms include solid or liquid state diapirism forceful dilation of country rocks and passive stoping i type granites are common and include early and late tectonic intrusions the widespread occurrence of i type granodiorite and monzogranite probably derived by partial melting of lower continental crust or subducted oceanic crust suggests a continental margin setting for the belt alkalic quartz diorite occurs as rounded enclaves in granodiorite and is enriched in ba rb sr ce la p and f which suggests a mantle derived volatile component these quartz diorite melts may have formed by partial melting of metasomatized mantle or alternatively mantle degassing may have lowered solidus temperatures in the source region and thus induced melting emplacement of hot volatilerich quartz diorite melts into the lower crust may have lowered solidus temperatures in the source rocks for granodiorite and monzogranite recent models for archaean gold mineralization suggest that auriferous fluids contained co 2 derived from lower crustal or mantle sources in the bardoc coolgardie area co 2 may have been flushed out during partial melting of the lower continental crust however the origin of the gold in the mineralizing fluids requires some other explanation because gold mineralization is generally a late stage event and took place over a considerably shorter time interval than the formation and emplacement of i type granites

melting of continental crust during subduction initiation a case study from the chaidanuo peraluminous granite in the north qilian suture zone the chaidanuo granite batholith is a similar to 500 km 2 homogeneous high level intrusion in the north qilian oceanic suture zone three types of enclaves have been recognized including 1 supracrustal xenoliths 2 biotite gneiss that represents restite of the upper crustal melting and 3 coeval mantle derived mafic magmatic enclave mme the batholith consists dominantly of peraluminous biotite monzogranite with sio2 69 73 wt and a cnk 1 05 1 28 and shows geochemical affinity with the upper continental crust e g enrichment of large ion lithophile elements liles k rb u th pb depletion of high field strength elements hfses nb ta ti p eu and sr and enriched sr sr 87 sr 86 i 0 731 to 0 744 nd epsilon nd t 6 0 to 7 1 isotopes zircon u pb dating indicates that this batholith formed at 516 505 ma coeval with the mmes 510 ma which represent the early stage of seafloor subduction in the north qilian suture zone the hf isotopic composition of the mme epsilon hf t 6 0 to 2 1 is more depleted than that of the host granite epsilon hf t 14 8 to 4 7 suggesting mixing of mantle and crust derived melts the inherited zircon cores in the host granite yield an age peak at similar to 750 ma with a few detritals of 591 1683 ma zircons from a biotite gneiss enclave yield a protolith age of 744 ma and a metamorphic melting event at 503 ma sr nd isotopic modeling reveals that the batholith was generated by melting of neoproterozoic granitic rocks with the addition of 10 18 mantle derived magma therefore peraluminous granite can be produced by melting of crustal materials heated by mantle derived magmas during the early stage of subduction initiation at the site of a prior passive continental margin c 2014 elsevier ltd all rights reserved

high frequency cyclicity milankovitch and millennial scale in slope apron carbonates zechstein upper permian north east england the upper permian zechstein slope carbonates in the roker formation zechstein 2nd cycle carbonate in north east england consist of turbidites interbedded with laminated lime mudstone studies of turbidite bed thickness and relative proportion of turbidites percentage turbidites in 20 cm of section reveal well developed cyclicities consisting of thinning upward and thickening upward packages of turbidite beds these packages are on four scales from less than a metre up to 50 m in thickness assuming that the laminae of the hemipelagic background sediment are annual allows the durations of the cycles to be estimated in addition counting the number and thickness of turbidite beds in 20 cm of laminated lime mudstone which is approximately equivalent to 1000 years each lamina is 200 m gives the frequencies of the turbidite beds the average thicknesses and the overall sedimentation rates through the succession for 1000 year time slots figures obtained are comparable with modern rates of deposition on carbonate slopes the cyclicity present in the roker formation can be shown to include milankovitch band ca 100 kyr short eccentricity ca 20 kyr precession and ca 10 kyr semi precession cycles and sub milankovitch millennial scale cycles 0 7 to 4 3 kyr eccentricity and precession scale cycles are related to highstand shedding and relative sea level change caused by milankovitch band orbital forcing controlling carbonate productivity the millennial scale cycles which are quasi periodic probably are produced by environmental changes controlled by solar forcing i e variations in solar irradiance or volcanic activity most probable here are fluctuations in carbonate productivity related to aridity humidity and or temperature changes precession and millennial scale cycles are defined most strongly in early transgressive and highstand parts of the larger scale short eccentricity cycles the duration of the roker formation as a whole can be estimated from the thickness of the laminated lithotype as ca 0 3 myr

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

wave power variation in the near shore regions abstract wave power variation in the near shore regions has been calculated for non breaking waves using an analytical formulation and an explicit solution bottom friction refraction and shoaling effects have been considered in the analysis the model has been extended to the analysis of random waves

peraluminous i type granites abstract s type granites always contain more al than the amounts of na ca and k in the rock required to form feldspars primarily owing to their derivation from source components that had previously been weathered those rocks are therefore always saturated in al or peraluminous many i type granites are also peraluminous despite i type source rocks typically not being saturated in al it has previously been suggested that this may result from the fractional crystallisation of amphibole however data from compositionally zoned high temperature plutons in the lachlan fold belt show that it is difficult to generate large quantities of peraluminous melt by removal of amphibole most of the i type granites 95 in the lachlan fold belt formed at lower temperatures and almost half of those rocks for which bulk chemical compositions are available are peraluminous among these granites there are 98 separate suites for which there are chemical data for two or more samples with 47 suites that include both metaluminous more mafic and peraluminous more felsic compositions the origin of those peraluminous compositions is fundamental to any understanding of i type granite petrogenesis in this region compositional variations caused by the assimilation or by partial melting of supracrustal rocks are very small as the isotopic variations within these rocks are dominantly between different suites not within suites the partial melting of more mafic source rocks rather than the fractional crystallisation of more mafic magmas is favoured for the origin of these rocks partial melting is the most likely process involved in the petrogenesis of felsic granites where broadly granodioritic monzogranitic batholiths are associated with lesser amounts of tonalite and very minor amounts of mafic rock experimental studies have shown that the melts generated by the partial melting of basaltic to andesitic rocks under crustal conditions are mostly peraluminous during the dehydrational melting of i type granite source rocks at pressures below the garnet stability field biotite and amphibole melt incongruently to yield pyroxenes the excess al is incorporated into the felsic liquid resulting in the generation of peraluminous melts in this instance the excess al in felsic i type granites is a function of the melting process and unrelated to the bulk composition of the source the observed gradation from peraluminous felsic granites to metaluminous compositions in less felsic rocks in largely isotopically closed systems could happen in two ways at higher temperatures of partial melting ca and other components of clinopyroxene could dissolve in the melt with the melt eventually becoming metaluminous alternatively minerals residual from partial melting dominantly pyroxenes and plagioclase could be incorporated in suspension in the melt so that the resulting bulk magma is metaluminous examples of these two extremes and of intermediate cases are well developed among the granites of southeastern australia

taiwan as a witness of repeated mantle inputs srndo isotopic geochemistry of taiwan granitoids and metapelites to aid a better understanding of the crustal evolution of se china isotopic studies of mid cretaceous granitoids and associated late paleozoic metapelites of the basement complex of taiwan have been undertaken initial nd values and 87sr86sr ratios for the granitoids range from 12 to 1 and 0 7051 to 0 7108 respectively suggesting a heterogeneous nature of their protoliths furthermore these initial nd and sr isotopic ratios define a covariant array lying between those of nearby metabasites and metapelites this indicates that the sources of granitoids could well be two component mixtures of a depleted component of mantle origin fresh to altered oceanic crust with nd 11 and 87sr86sr 0 703 0 708 represented bythe adjacent amphibolite and an enriched continental component nd 12 and 87sr86sr 0 712 respresented by the metapelites with the latter making up from 15 to 60 oxygen isotope data are also consistent with this mixing model nd model ages with respect to the depleted mantle reservoir tdm for taiwan granitoids range from 0 9 to 1 5 ga these model ages are slighlty younger than those of the s type granitoids of se china and world wide phanerozoic sedimentary rocks implying a significant contribution from juvenile material similar to the granitoids taiwan metapelites are also heterogeneous in nd and sr isotopic compositions with each body possessing its own characteristic ranges nd crustal residence ages tdm for taiwan metapelites range from 1 1 to 1 6 ga which are younger 1 5 2 3 ga than those of the paleozoic sediments of south china thus the oldest sediments in the taiwan basement received not only recycled continental crustal material but also fresh mantle input therefore taiwan is a good witness of at least three episodes of fresh mantle inputs to the crust of the eurasian continent the ongoing accretion of the intra oceanic luzon arc the mesozoic event recorded in granitoids and the paleozoic event recorded in metapelites

generation of leucogranites via fractional crystallization a case from the late triassic luoza batholith in the lhasa terrane southern tibet abstract leucogranites are important in understanding intracrustal differentiation and regional tectonic evolution but how these rocks form remains a matter of much debate the luoza batholith in the central lhasa subterrane provides an important opportunity to address these issues as this batholith consists of normal calc alkaline s type granodiorites group 1 and highly fractionated s type leucogranites group 2 laser ablation inductively coupled plasma mass spectrometry zircon u pb dating indicates that these rocks were emplaced at ca 221 205 ma the group 1 samples ca 205 ma have low sio2 content 64 67 wt and low differentiation index values di 75 76 and are slightly depleted in ba p sr and ti compared to the group 2 samples ca 221 ma and 213 ma which have high sio2 content 74 75 wt high differentiation index values 91 94 and are significantly depleted in ba p sr and ti samples from group 1 and group 2 exhibit similar zircon ehf t values 15 6 to 1 4 both of which are significantly higher than melts from the pure ancient basement in the central lhasa subterrane 20 5 to 10 6 the group 1 samples can be interpreted as having been derived from the partial melting of metagreywacke within the ancient basement in the central lhasa subterrane with contributions from mantle or juvenile crust derived components whereas the group 2 samples may have formed via varying degrees of fractional crystallization of different minerals e g plagioclase k feldspar biotite zircon allanite monazite titanite and apatite from the parental magmas represented by the granodioritic samples in group 1 in shallow crustal magma chambers in combination with sedimentary records the high temperature and low pressure conditions indicated by the group 1 samples can be geodynamically linked to a back arc extensional setting in response to the southward subduction of the bangong nujiang tethys ocean seafloor our work implies that fractional crystallization is likely a feasible mechanism for the development of leucogranites and for explaining the compositional diversity of the granite during intracrustal differentiation

do co2 charged fluids contribute to secondary porosity creation in deeply buried carbonates abstract carbonate dissolution by acidic co2 charged fluids is one possible mechanism leading to the creation of burial porosity the late permian carbonates of the lower saxony basin nw germany are a suitable target to study the influence of such co2 charged fluids on porosity evolution the so called zechstein 2 carbonates ca2 consist of alternating dolomitic and calcitic intervals and contain locally very high amounts of co2 80 and variable amounts of h2s in reservoir gas and vein cement hosted fluid inclusions composition and isotope data from fluid inclusions suggest that the co2 is sourced from the thermal decomposition of underlying devonian carbonates far reaching fault systems connect the devonian co2 source with the permian ca2 reservoir while thick rock salt deposits above the zechstein 2 carbonates prohibit an influence of surface derived meteoric fluids the aim of the study is to evaluate the contribution of co2 on carbonate dissolution seven wells were preferentially sampled along mineral veins which are interpreted as the preferred migration pathways for the present gas classic petrography methods such as transmitted light microscopy and cathodoluminescence were combined with fluid inclusion analysis and porosity data petrographic analysis reveals no great impact of the massive co2 presence on porosity creation as fluids get quickly saturated with respect to ca2 minor vuggy porosity is associated with fractures in only one of the studied wells but the dominant porosity types are early diagenetic fabric selective oomoldic and intercrystal porosity to evaluate whether the porosity values are higher than usual a comparison with a global porosity dataset is included which however shows no increase in average porosities compared to global values the results of this case study suggest that the contribution of co2 alone on carbonate dissolution and therefore reservoir quality is negligible as long as other processes such as late dolomitization or pyrite formation by thermochemical sulphate reduction derived h2s are absent

petrogenesis of the early paleozoic strongly peraluminous granites in the western south china block and its tectonic implications abstract strongly peraluminous sp granites have a cnk molecular al 2 o 3 cao na 2 o k 2 o ratios 1 1 indicating a predominant origin from the partial melting of metasedimentary rocks however an increasing number of studies have documented that mantle derived magmas can also be involved in the petrogenesis of some sp granites this is the case in the dulong batholith in the southeastern yunnan province southwestern south china block which is typically composed of sp granitic rocks with high a cnk values 1 1 zircon u pb dating of four samples from this batholith yielded consistent crystallization ages of ca 430 ma synchronous with the widespread late orogenic magmatism including s and i type granites and mafic igneous rocks in the wuyi yunkai orogen south china block scb all the granites have fractionated ree patterns la yb n 1 28 12 3 and conspicuous negative eu anomalies eu eu 0 07 0 43 with a similar depletion in hfse nb zr hf p ba and sr suggesting that these granitic magmas had a dominantly crustal source likely the neoproterozoic metasedimentary rocks i e the danzhou or banxi groups that are dominated by pelitic rocks with minor interlayered siltstones in the western yangtze block however their zircon hf isotopic results also reveal an important input of the mantle derived melts into their parental magma taken together their geochemical and isotopic compositions reflect a derivation by magma mixing between the crust and mantle derived 10 in volume magmas their chemical variations resulted from the fractionation process during the emplacement from the magma chamber after magmatic mixing in conjunction with regional data within the scb it is most likely that the magmatism younger than 435 ma was generated in a post collisional extensional regime related to the partial delamination of an overthickened lithospheric mantle root without lower crust

do s type granites commonly sample infracrustal sources new results from an integrated o u pb and hf isotope study of zircon in contrast to i type granites which commonly comprise infracrustal and supracrustal sources s type granites typically incorporate predominantly supracrustal sources the initial aim of this study was to identify the sources of three scottish caledonian 460 ma s type granites kemnay cove and nigg bay by conducting oxygen u pb and hf isotope analyses in zircon in order to characterise one potential end member magma involved in the genesis of the voluminous late caledonian 430 400 ma i type granites field whole rock geochemical and isotopic data are consistent with the generation of the s type granites by melting their dalradian supergroup country rocks while hf isotope compositions of magmatic zircon u pb data of inherited zircons and high mean zircon 18o values of 9 0 2 7 2sd and 9 8 2 0 for the kemnay and cove granites support this model the nigg bay granite contains zircons with much lower 18o values 6 8 2 1 similar to those found in scottish i type granites this suggests that the nigg bay granite contains low 18o material representing either altered supracrustal material or more likely an infracrustal source component with mantle like 18o mixing trends in plots of 18o vs ehf for s type granite zircons indicate involvement of at least two sources in all three granites this pilot study of scottish caledonian s type granites demonstrates that while field and whole rock geochemical data are consistent with local melting of only supracrustal sources the oxygen isotopic record stored in zircon reveals a much more complex petrogenetic evolution involving two or more magma sources

displaced carbonates in the zechstein of the uk north sea abstract the cored zechstein 2 interval of amoco well 38 24 1 drilled on the southern margin of the mid north sea high contains deformed conglomeratic and brecciated dolostones which are interpreted as displaced distal shelf sediments redeposited in deeper water the displaced dolostones indicate disruption and sliding of consolidated rock down a slope accompanied by slumping of semi consolidated sediment minor collapse brecciation also occurred as a result of the partial removal of underlying evaporites such features have not hitherto been described from cored wells in the uk north sea nor have their petrophysical attributes been discussed the best reservoir properties occur in the slumped deposits showing plastic deformation brecciated beds have unpredictable and wide ranging porosity and permeability values which are attributable to variable anhydrite cementation and clasts with different textures and very variable fabric displaced zechstein carbonates on or at the foot of unstable palaeo slopes for example in the vicinity of the mid north sea high can develop moderately attractive reservoir characteristics and might in places be thick enough to be of economic importance

numerical model for nonstationary shallow water wave spectral transformations a nonstationary wave transformation model is developed based upon a finite difference scheme this model computes spatial and temporal distributions of wave spectral density in shallow water areas with irregular bottom topography current knowledge of the dynamic and kinematic processes is incorporated into the model which include the usual wave refraction and shoaling effects as well as nonlinear dissipative processes breaking bottom friction and a constraint on total energy growth in a depth limited situation and local wind wave generation processes a combined phillips miles model another important feature of the model is the inclusion of current effects spatial and temporal current distributions can be introduced as input conditions based upon this model a number of sample computations are given to examine the characteristics of nonstationary wave transformation processes finally one set of wave data collected in the north sea during the marsen project is used to compare with numerical model computations

a hybrid origin for lachlan s type granites the murrumbidgee batholith example the murrumbidgee batholith is typical of other composite s type granite batholiths in the lachlan fold belt lfb of southeastern australia consisting of discrete peraluminous cogenetic granite suites however it contains a unique suite murrumbucka at its southern extremity that has chemical and petrological features transitional with metaluminous i type granites previous detailed structural and metamorphic studies have shown that the batholith is tilted northward exposing subvolcanic plutons in the north and root zones in the south originally located at depths of not vert similar10 km a transition from mafic foliated sheet like granites in the south to felsic generally less foliated homogeneous granites in the north is consistent with magma ascent via subvertical structurally controlled sheets to emplacement in an overlying magma chamber in the inferred root zones the murrumbucka suite hosts migmatitic metasedimentary and gabbroic rocks both of which have transitional contacts and show evidence for mafic felsic interaction with the murrumbucka suite the migmatites extend southward to become part of the high t low p cooma metamorphic complex which contains a core of heterogeneous remobilised diatexitic granite cooma suite lenses of which also occur throughout the southern deeper parts of the murrumbidgee batholith the composition of the most mafic rocks from the batholith lies on a chemical tie line between cooma suite granites and the gabbros for almost all elements this chemical coincidence is interpreted to reflect derivation of parental murrumbidgee s type granite magmas by bulk mixing between a felsic crustal and mafic mantle derived component consistent with sr and nd isotopic results and field observations based on the tie lines and simple numerical modelling the murrumbucka suite is estimated to be a 50 50 mix of mantle and crustal derived magmas whereas the more peraluminous and widespread clear range suite which is very typical of lachlan s type granites is modelled as a 40 60 mix chemical variation trends diverge from the mixing lines and suggest that much of the fractionation process operated after mixing mixing occurred within sheets during the ascent of the magmas whereas fractionation was the dominant process generating chemical diversity during emplacement in the magma chamber generation of the s type granites probably occurred in an extensional tectonic environment

a rift drift delamination model of continental evolution palaeozoic tectonic development of eastern australia the adelaide lachlan and new england fold belts of eastern australia record the continental growth of eastern gondwanaland during the palaeozoic the new england fold belt nefb represents a tectonic collage formed by subduction accretion during the late paleozoic but contains remnants of subduction related rocks that date from the cambrian the lachlan fold belt lfb developed inboard from the nefb initially as an amalgam of proterozoic continental and cambrian oceanic fragments that formed by rift and drift at the leading edge of eastern gondwanaland convergent tectonism at 500 ma welded the fragments to the craton and formed the adelaide fold belt oceanward dispersal of detritus across the lfb produced an overlap assemblage of quartzose ordovician turbidites and a new subduction zone developed at the eastern margin the tectonic setting was similar to the modern philippines plate of the western pacific behind the arc silurian devonian convergent tectonics converted the 1700 2000 km wide continental margin of the proto lfb into a 750 km wide thin skinned fold magmatic belt within 60 ma the driving force was delamination which produced a ubiquitous basaltic underplate that generated 1 regional low p metamorphism 2 local anticlockwise p t t paths and crustal scale isobaric cooling 3 voluminous syn to late tectonic granitoids emplaced at rates approximately twice that of modern arcs and 4 normal thickness crust despite an average of 60 shortening delamination occurred in two separate areas originally 1000 km apart first in the eastern then in the western part of the lfb the lfb and its northern counterpart the thomson fold belt represent approximately one fifth of the australian continent and evolved from dispersed fragments into stable continental crust in 300 ma such rapid growth rates are typical of the 2 7 2 5 ga and 1 9 1 7 ga periods when voluminous widespread granitoids and large turbidite dominated low p metamorphic belts were produced in settings that are not obviously subduction related therefore a similar process of rift drift delamination riddel tectonics may have periodically operated throughout earth history

formation of the jurassic south china large granitic province insights from the genesis of the jiufeng pluton abstract the magma source and thermal regime for the formation of large granitic provinces lgps have been the subjects of much debate as mineralogical geochemical and isotopic variations of plutonic rocks preserve records of crustal thermal evolution the jiufeng pluton was comprehensively studied to gain insights into material and heat sources and tectonic process in the formation of the south china lgp sims zircon u pb analyses of a biotite granite 158 9 1 3 ma three two mica granites stage i 159 7 1 2 ma stage ii 158 6 1 2 ma and 156 8 1 2 ma and a muscovite granodiorite 159 0 4 4 ma of the jiufeng pluton suggest that they are coeval and were emplaced in a short period of no more than 5 3 m y limited variations in whole rock nd isotope end t 12 6 to 9 5 and zircon hf o isotopes ehf t 12 0 to 6 3 18 o 6 8 9 4 suggest that the jiufeng pluton was mainly derived from melting of a common metasedimentary source possibly with a minor basaltic contribution we consider the geochemical variations of the jiufeng pluton are primarily a result of incremental assembly of magma batches produced from rapid step like transition from fluid saturated to fluid absent melting of the source the muscovite granodiorite with high na 2 o 3 80 wt k 2 o na 2 o 1 is interpreted to have been produced by fluid saturated melting at low temperature 650 c high p 2 o 5 0 09 0 17 wt zircon saturation temperature t zr 769 816 c and la yb ratios 8 4 55 8 of the stage ii two mica granite support its formation from high temperature 800 c biotite dehydration melting whereas lower p 2 o 5 zr 685 742 c and la yb

the pb sr nd isotope geochemistry of some recent circum mediterranean granites pb sr and nd isotopic compositions have been analyzed in recent granites from northern africa northern italy and greece lead isotope compositions of k feldspars are rather homogeneous and cluster close to the modern lead of stacey and kramers 1975 but with slightly higher207pb 204pb and208pb 204pb ratios the cyclades samples however have higher206pb 204pb ratios addition of mantle derived lead was probably very limited which supports a quasi closed system evolution of this element in the continental crust the sr nd data fall in the enriched part of the143nd 144nd vs 87sr 86sr diagram and define a smooth hyperbolic mixing curve over a wide area straddling different orogens most granites may be accounted for by a binary mixture between a recycled crustal component and a depleted mantle like component no correlation is observed between either pb and sr or nd isotopic ratios or any isotopic ratio and major element contents quantitative modelling suggests that two cases fit the sr and nd characteristics of these granites they both require anatexis of the crust on a scale large enough to average the isotopic properties of heterogeneous terranes in the first case the mantle derived component may be represented by differentiated island arc type magmas and the granites result from mixing these magmas with anatectic melts in the second case mantle derived igneous rocks such as obducted ophiolites are part of the crustal source and their variable involvement in the anatectic process causes isotopic variations

fractional crystallization in open systems of variable composition correlations between element concentrations abstract fractional crystallization in open systems is modelled in a general mathematical form the estimation of element concentrations in liquid and solid phases is done by means of a system of coupled nonlinear first order differential equations with special physically founded assumptions on distribution coefficients and source terms in the equations several special cases can be derived which are known in the literature as an application correlations between solid phase concentrations of major elements trace elements and isotopes are derived which can be used for the interpretation of geological processes especially the changes of strontium and rubidium concentrations of magmatic rocks are discussed in the progression of magma differentiation in a second example the evolution of trace elements in the west erzgebirge g d r as an open crystallizing magmatic system is discussed

origin of enclaves in s type granites of the lachlan fold belt abstract the more mafic s type granites of the lachlan fold belt contain a distinctive assemblage of lithic inclusions of deep crustal origin two types predominate the schistose enclaves and the microgranular enclaves there is also a small proportion of fragments of local country rock all the features of the schistose enclaves are consistent with an origin as lithic restite fragments from the source their ubiquity in the mafic s type granites and absence from both felsic s type granites and i type granites conform with such an origin the argument that these enclaves are not in chemical equilibrium with the host granite because they do not complement its composition is not valid since they represent less fertile parts of the source that had different compositions that as a result melted to a lesser extent models that derived these enclaves from regions of the crust above the zones of partial melting so that they are not restites are complex unnecessary do not conform with their ubiquity in the more mafic s type granites and are not consistent with their chemical compositions the origin of the microgranular enclaves is controversial in most s type granites these enclaves have been recrystallized to a similar mineral assemblage to the host granite with a higher proportion of biotite in a few places such material is seen to be forming by recrystallization of material in the core of the enclave which has the assemblage quartz calcic plagioclase orthopyroxene cordierite biotite with accessory ilmenite sulfide and apatite all of the microgranular enclave cores show pseudo doleritic texture in which calcic plagioclase crystals an60 and orthopyroxene crystals project into or are enclosed by quartz large plagioclase crystals are zoned with some core compositions as calcic as an94 the low na contents of the microgranular enclaves are not consistent with an igneous origin we consider that these enclaves were derived by metamorphism of calcareous mudstones or argillaceous limestones the pseudo igneous textures result from the presence of a partial melt during metamorphism an analysis of a calc silicate lens of upper amphibolite grade from the wilsons group of victoria land antarctica is remarkably similar in composition to the microgranular enclaves from lachlan fold belt s type granites we suggest that rocks equivalent to that group which is of appropriate age and general composition were the source rocks for the s type granites of the lachlan fold belt

mesozoic dissolution tectonics on the west central shelf uk central north sea abstract 3 d seismic mapping of the upper jurassic kimmeridge clay formation on the west central shelf in the central north sea reveals a complex fault array which is constrained by seismic interpretation and well control to be of late jurassic early cretaceous age fault shapes in plan view range from linear to circular linear fault lengths are 200 300 m to 5 km the strongly curved and circular faults range in diameter from 100 1000 m fault trends are apparently random and display no correlation in location or trend with basement sub zechstein structures there is however a strong link between this fault pattern and the structure of the top zechstein top salt surface linear faults occur at the edges of elongate salt walls and the circular faults lie directly above structures which have been interpreted here as tall steep sided salt chimneys the salt chimneys are present only in the thick elongate minibasins of triassic sediment which lie between the salt walls it is argued that salt dissolution controls the timing location orientation and shape of the late jurassic early cretaceous faults a model is provided to account for the development of both salt walls and chimneys we suggest that early triassic karstification of the zechstein evaporites led to development of an array of circular collapse features during the ensuing episode of triassic halokinesis which led to minibasin subsidence and salt wall growth salt passively intruded the circular collapse features within the subsiding minibasins to form narrow salt chimneys the resulting array of salt walls and chimneys was subject to dissolution during subsequent subaerial exposure and the late jurassic marine transgression of the basin creating the observed fault array prior to sealing of the salt from circulating groundwater by compaction of the upper jurassic and lower cretaceous shales which blanket the area

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

palaeozoic arc growth deformation and migration across the lachlan fold belt southeastern australia abstract the palaeozoic lachlan fold belt lfb is a low pressure metamorphic belt characterized by greenschist facies rocks and infolded volcanic sequences which indicate that the belt has not undergone substantial uplift at any stage porphyroblast matrix relationships in one of the highest grade metamorphic zones of the lfb the omeo complex indicate that the thermal peak was reached before or was synchronous with the earliest deformation similar to that in high grade metamorphic zones of the northern arunta inlier central australia in both areas the metamorphism is of low p high t type centred on major granite intrusions as regional aureoles and characterized by anti clockwise p t t paths however in the outer lower grade parts of the aureoles peak metamorphic conditions post date the earliest deformation this diachronous relationship indicates that 1 outward migration of a thermal front was centred on major granitoid intrusions batholiths 2 deformation propagated outward more rapidly than migration of the thermal front and 3 plastic and ductile deformation began only after heating around the batholiths thus orogeny was initiated after and localized by heat focusing in the mid crust associated with batholith emplacement therefore the early deformation is a result of thermal softening it is typically subhorizontal ductile shear at mid crustal levels but is characterized by upright to inclined folds at upper crustal levels in the latter environment the typically discordant contact aureole plutons are often interpreted as post tectonic granitoids but they were part of the ongoing mid crustal thermal perturbation that induced regional greenschist facies metamorphism which overprinted the early formed upright folds as it migrated to upper crustal levels orogeny migrated generally eastward through the lfb it began with the early silurian benambran orogeny centred on the wagga metamorphic belt wmb and terminated with the carboniferous kanimblan orogeny which was most intense in the hill end trough eastward migration of orogeny across central victoria part of the west lfb began in the ballarat bendigo zone during the early devonian and terminated in the melbourne zone in the middle devonian orogeny was centred on the meridional batholiths of the lfb each of which are considered to represent the transitory axis of an ancient magmatic arc stepwise but generally eastward arc migration caused the eastward migration of orogeny a tectonic model based on the modern southwest pacific arc system can be applied to the lfb following cambrian intra oceanic arc growth associated with west dipping subduction an ordovician marginal sea developed partly on stretched cambrian crust and was flooded by an extensive turbiditic wedge closure of the eastern part the east lfb began in the early silurian after a magmatic arc developed over the wmb possibly associated with an east dipping subduction zone after re establishment of west dipping subduction in the middle silurian absolute motion retreat of the upper australian plate caused by oblique plate convergence resulted in dextral transtension and the generation of siluro devonian inter arc and back arc basins transient compression resulted in deformation along the magmatic arc and induced formation of a new outboard eastward arc system periodic compression within the evolving arc and back arc system resulted in a series of east younging east verging linear siluro devonian fold and thrust belts which were localized adjacent to elongate batholiths that represent the relict arc systems local westward jumps in deformation and plutonism occurred the most significant is the 600 km westward jump into the west lfb caused by closure of the remainder of the passive ordovician back arc basin melbourne and bendigo ballarat zones west dipping subduction beneath the basin produced a low pressure fold thrust belt similar to the east lfb though the granitoids have a more primitive isotopic character indicating closure of thin dominantly oceanic crust in the early to middle devonian localized deformation induced by thermal softening of the crust within magmatic arcs that have developed on earlier passive margins is likely to produce anticlockwise p 7 t paths and may be a typical feature of southwest pacific style tectonism

geochronology geochemistry and isotope compositions of piaochi s type granitic intrusion in the qinling orogen central china petrogenesis and tectonic significance abstract s type peraluminous granite can crop out in various tectonic settings the paleozoic piaochi granitic intrusion is a large s type peraluminous intrusion located in the north qinling orogen and has important implication for its tectonic evolution though intensively studied the age and tectonic setting of this intrusion are still controversial in this study we carried out an integrated study of zircon u pb age major and trace elements and sr nd hf o isotope compositions for the piaochi intrusion with aims to constrain its petrogenesis and tectonic significance sims and la icpms u pb zircon data obtained from magmatic zircons indicate that the piaochi intrusion was emplaced at 473 4 ma and contained ca 490 ma inherited zircons the granite samples from the piaochi intrusion show typical s type characteristics such as the relatively moderate aluminum saturation index 1 00 1 08 low zirconium saturation temperatures occurrences of muscovite and high zircon 18 o values 8 70 to 9 54 the relatively low sm nd 0 13 0 20 and feo t mgo ratios 2 21 3 9 suggest that the granites are unfractionated the geochemical compositions reveal that they were derived from partial melting of a clay poor but plagioclase and biotite rich psammitic source similar to metasedimentary rocks outcropping in the north qinling unit moreover the piaochi granites are moderately depleted in eu and heavy rare earth elements and have relatively high la yb n values 22 8 56 8 implying a high pressure plagioclase poor and garnet rich residual assemblage the piaochi granites have high and variable initial 87 sr 86 sr ratios 0 72167 0 72511 and low e nd t from 10 23 to 8 71 values with two stage nd model ages t dm2 of 1 91 2 03 ga which are comparable with those of supracrustal materials in the north qinling unit in addition our results show that the ca 470 ma magmatic zircons display a narrow e hf t array within those of the inherited cores these imply that the piaochi granites inherited their isotopic characteristics wholly from their sources and the hf isotopes might have been differently homogenized during the partial melting our new zircon u pb ages indicate that the piaochi granites were emplaced after the climax of the uhp metamorphism coeval with later retrograde metamorphism during exhumation therefore we suggest that the formation of the early paleozoic piaochi intrusion was triggered by the exhumation of the uhp rocks

wave spectral transformation measurements at sylt north sea abstract wave spectra were measured in the nearshore region extending approximately 900 m from the shore at the island of sylt north germany in the north sea the measurement covered two periods one in may 1976 when the sea condition was considered normal in this region and the other period was during a storm in september 1978 the field results are presented and compared with numerical computations for energy transformation in shallow water based on a numerical model developed by shiau and wang 1977 the field data supported the validity of the numerical model the results suggest that prior to wave breaking the transformation of wave components is mainly influenced by shoaling and refraction the bottom frictional effect could also be important in the energy containing range after breaking turbulent generation due to wave instability seems to be the dominant mechanism of energy dissipation

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

the tynong pluton its mafic synplutonic sheets and igneous microgranular enclaves the nature of the mantle connection in i type granitic magmas in the lachlan orogen of south eastern australia the high level postorogenic 368 ma i type tynong pluton contains granitic to granodioritic rocks that crystallised from a variety of mainly crustally derived magmas emplaced in the shallow crust in an extensional regime the isotopic characteristics of the main plutonic rocks are relatively unevolved 87sr 86srt 0 705 0 706 and endt 0 4 to 0 6 suggesting source rocks not long separated from the mantle we infer that arc mafic to intermediate rocks and associated immature greywackes formed the main crustal source rocks and that these are located in the largely unexposed neoproterozoic cambrian selwyn block that forms the basement as exposed near its southern margin the pluton also contains minor pillowed sheet like intrusions of quartz dioritic rock that show mainly mingling structures with the enclosing granodiorites as well as some hybrid pods and fairly abundant igneous microgranular enclaves that we infer to have been derived from the quartz dioritic sheets despite this evidence of direct mantle input into the tynong magma system the main granodioritic series do not appear to have been formed by magma mixing processes of any i type granite in the region the tynong pluton has perhaps the most direct connection with mantle magmas nevertheless the main mantle connection here is probably in the mantle derived protolith for these crustal magmas and in the mantle thermal event that gave rise to melting of the deep crust in the selwyn block this degree of mantle connectedness seems typical for i type granitic rocks worldwide

origin of late mesozoic granitoids in the newly discovered zha shan porphyry cu district south qinling central china and implications for regional metallogeny abstract the newly discovered porphyry cu deposits in the south qinling belt sqb have not been well researched as compared with the large porphyry mo province in the southern north china block s ncb and the origin of granitoids associated with porphyry cu mineralization in the zha shan district sqb is poorly constrained here we present detailed zircon u pb geochronological whole rock elemental and sr nd isotopic data for important late mesozoic granitoid stocks associated with porphyry cu deposits in the zha shan district these data are used to constrain the age and the source of magmas that formed these granitoids and implication of regional metallogeny the new zircon la icpms u pb ages presented here indicate that the granitoids related to porphyry cu system at chigou beishagou shuangyuangou and yuanjiagou developed at 148 144 ma 144 ma 145 144 ma and 146 ma respectively these rocks are high k calc alkaline i type granitoids which are enriched in large ion lithophile elements e g th u and pb and light rare earth elements are depleted in nb ta and ti characterizing by wide variations in initial end t 3 8 to 9 5 and moderate radiogenic sr isotopes 87 sr 86 sr i 0 7046 to 0 7093 these features indicate that the magmas that formed the granitoids related to porphyry cu system in the zha shan district formed as a result of variable degrees of mixing between crustal and metasomatic lithospheric mantle the new zircon la icpms u pb ages in this study combined with previous published data suggest that regional scale late jurassic to early cretaceous granitoid stocks and associated porphyry cu and mo systems in both the s ncb and sqb formed almost contemporaneously with 147 139 ma porphyry mo deposits in the s ncb and 148 145 ma porphyry cu deposits in the sqb the cu related intrusions contained a greater contribution of lithospheric mantle component than the mo related intrusions in the east qinling orogeny

measurements of the evolution of ocean wave spectra due to bottom friction data from a field experiment in which seven wave measurement instruments were placed in a linear transect across the great australian bight are analyzed to determine the spectral decay which can be attributed to bottom friction since other processes such as atmospheric input nonlinear interactions whitecap dissipation refraction and shoaling will also be active the spectral wave model wam is used as an analysis tool explicitly taking these additional processes into account in the analysis the data show marked spectral decay across the shelf analysis reveals that the bottom friction coefficient c is not constant as often assumed in operational wave models the bottom friction coefficient varies approximately inversely with the wave induced bed velocity consistent with the predictions of previous laboratory data and eddy viscosity models it is possible that percolation may also be important in the region but the available data do not allow the relative contributions of bottom friction and percolation to be determined

strontium isotopic and chemical variations of the granitic rocks in the tsukuba district japan initial 87sr 86sr ratios major and trace element compositions have been determined for the paleogene granitic rocks in the tsukuba district japan isotopic ages strongly suggest that the granitic rocks seven units were continuously emplaced and solidified during a short time interval initial 87sr 86sr ratios for seven granitic units vary from 0 7082 to 0 7132 while sedimentary and metasedimentary country rocks have ratios at the time of granitic magma emplacement ranging from 0 7149 to 0 7298 continuous linear arrays for the granitic rocks in the diagrams of initial 87sr 86sr ratios versus some chemical parameters can be explained by either of following two processes one is the assimilation fractional crystallization afc process between the parental magma sio2 of 68 and initial ratio of 0 7078 and sedimentary country rocks and the other is magma mixing process between above parental magma and sediment derived acidic magma melt sio2 of 75 the high initial ratios 0 7078 0 7098 for basic rocks such as gabbro or diorite in the tsukuba district and the similar characteristics observed in the rocks of ryoke belt sw japan suggest that the parental magma had the same source region as the basic rocks probably the lower crustal source

cryptic sr and nd isotopic variation across the leinster granite southeast ireland rb sr isotope whole rock data from the end caledonian leinster batholith define an errorchron age of 464 26 ma appreciably older than the accepted emplacement age of c 405 ma this anomalously old age is the consequence of a highly variable initial sr isotopic composition initial nd ratios and t dm model ages also show a wide range of values however these isotopic variations are neither randomly distributed nor related to petrographic changes but instead reflect in a simple way geographic position about the axis of the batholith the isotopic pattern revealed in the leinster batholith means that isochron ages obtained from s type granites may be largely dependent on the sampling scheme adopted the variable isotopic composition of the granite most likely resulted from either a heterogeneous metasedimentary source or hybridization of coeval dominantly crustal melts

u pb zircon studies of mid crustal metasedimentary enclaves from the s type deddick granodiorite lachlan fold belt se australia

the nd and sr isotopic composition of i type microgranitoid enclaves and their host rocks from the swifts creek pluton southeast australia abstract initial nd and sr isotopic compositions have been determined for microgranitoid enclaves and their host rocks from the siluro devonian swifts creek pluton within the lachlan fold belt of southeastern australia enclaves are of quartz dioritic to tonalitic composition and their textures support an igneous origin host rocks range from tonalite to granite the isotopic data form an array in nd 87 sr 86 sr space with enclaves systematically displaced towards higher nd and lower 87 sr 86 sr values enclaves range in nd t 405 ma from 7 3 to 3 1 with a narrow range in 87 sr 86 sr from 0 70613 to 0 70718 whereas host rocks range from 9 0 to 6 4 and 0 70761 to 0 70946 in nd and 87 sr 86 sr respectively the isotopic relations rule out simple crystal liquid fractionation or restite unmixing alone as the major genetic link between enclaves and host rocks the data are also incompatible with an origin of the enclaves by crystal accumulation or liquid immiscibility instead mixing between a mafic mantle derived and a crustal derived end member to generate the host rock enclave spectrum is compatible with the data because the initial isotopic ratios of enclaves and host rocks are well within the range of crustal rocks we favour the alternative view that both enclave and host rock magmas are of crustal origin consequently we avoid extrapolations to hypothetical end members we suggest that the enclaves from the swifts creek pluton are derived by partial melting of a mafic lower crust and mixed at or near the site of magma generation with a chemically less primitive and isotopically more evolved component to generate the enclave and host rock spectrum the isotopic heterogeneities within the enclave and host rocks survived the superimposed effects of crystal liquid fractionation model ages tdm for enclaves and host rocks are almost identical averaging 1 7 and 1 6 ga respectively these model ages indicate that both the enclave and host rock protoliths were derived from a mantle reservoir during the proterozoic

origin of the granites and related sn and pb zn polymetallic ore deposits in the pengshan district jiangxi province south china constraints from geochronology geochemistry mineral chemistry and sr nd hf pb s isotopes the pengshan sn and pb zn polymetallic deposits are located in the south margin of the jiujiang ruichang jiurui district of the middle lower yangtze river metallogenic belt in south china four large deposits include huangjinwa zengjialong jianfengpo and zhangshiba the former three are sn dominant deposits which occur as stratiform orebodies in the contact zones of the pengshan granites and within the country rock strata whereas zhangshiba consists of stratiform pb zn orebodies within the precambrian metasedimentary strata in this study we present results on zircon u pb ages major and trace elements and mineral chemistry as well as sr nd hf isotope data of the granites pb and s isotopes of both the sn dominant and pb zn dominant deposits and u pb dating of cassiterite from the pengshan district shrimp and la icp ms zircon u pb dating shows that the pengshan granites were emplaced in the early cretaceous 129 128 ma which is in good agreement with the u pb dating 130 128 ma of cassiterite from the jianfengpo sn deposit the pengshan granites consist mainly of weakly peraluminous highly fractionated i type affinity granitic rocks detailed elemental and isotopic data suggest that the granites formed by partial melting of mesoproterozoic metamorphic basement materials with minor input of mantle derived melts the mineral chemistry of biotite demonstrates that the pengshan granitic magma had a low oxygen fugacity thereby precluding the tin dominantly partitioning into the rock forming silicate minerals and favoring accumulation in the exsolved residual liquid during magma crystallization stages sulfur isotopes show a relatively heavy sulfur isotopic composition from 5 8 to 17 6 and no difference for sulfur isotopes between the sn deposits 5 8 13 4 huangjinwa zengjialong jianfengpo and the pb zn deposit mostly 7 1 13 0 except for one 17 6 zhangshiba the sulfur isotope data of pyrite from the host sedimentary rocks show relatively higher 34s values of 22 7 28 7 lead isotopes indicate that the granites have higher 206pb 204pb 207pb 204pb and 208pb 204pb ratios than the host precambrian metasedimentary rocks and the sulfide minerals from the orebodies fall in between them again there is no difference for pb isotopes between the sn deposits huangjinwa zengjialong jianfengpo and the zhangshiba pb zn deposit the coincidence in s and pb isotope compositions for sn and pb zn deposits suggests that similar sources for these mineralization possibly derived from a mixed source of the granitic magmas and the precambrian metasedimentary rocks these data therefore favor of a magmatic hydrothermal origin for both the sn and pb zn polymetallic mineralization in the pengshan district

chilled margins and commingling of magmas in the bressanone brixen hercynian granodiorites eastern alps northern italy abstract the brixen hercynian pluton is the result of a multiple intrusion of crustal anatectic magma granodiorite granites and two mica cordierite bearing leucogranites and subcrustal magma gabbro diorites and fayalite bearing leucogranites some adjacent granodioritic stocks show chilled margins containing globular inclusions in the size of several centimetres of a coarse grained leucogranite the granodiorite margins also show narrow zoning with more acidic external borders this phenomenon is correlated to differentiated processes such as filter pressing and the soret effect which were active during the rise of these stocks the strong petrographic and chemical analogies between the globular inclusions of some chilled margins and the fayalite leucogranites suggest their common subcrustal origin the granodiorite containing these inclusions is of crustal origin the occurrence of globular inclusions inside it thus indicates only mechanical mingling between crustal anatectic and subcrustal magmas as shown by the absence of hybrids and chemical interactions

field study of wave attenuation on an offshore coral reef a major field experiment was conducted which obtained measurements of the attenuation and transformation of short gravity waves as they cross the windward edge of an offshore coral reef water level data were collected for over 3000 individual time series during a wide range of environmental conditions at the innermost measurement site which is located on the horizontal reef flat after the completion of wave breaking the upper bound of significant and maximum wave heights is limited to less than 40 and 60 of the reef flat water depth respectively as with significant wave height both the shape and energy level of the reef flat spectra are strongly affected by changes in reef flat water depth for higher tide levels the spectra on the reef flat closely mimic the corresponding incident spectra however the attenuation is greater for both lower frequencies and higher energy portions of the spectra this causes the reef flat spectra to be broader than those measured windward of the reef at lower water levels considerable energy losses due to wave breaking and bottom friction occur most of the energy loss comes from the vicinity of the spectral peak and energy shifts to harmonics of the peak of the spectrum can be seen

magma mixing and the production of compositional variation within granite suites evidence from the granites of southeastern australia granite suites are groups of plutons possessing characteristic features that are a result of their derivation from source material of a specific composition variation within suites has been ascribed to a variety of processes magma mixing or mingling is a popular hypothesis generally proposed in terms of blending between a crustal melt and mafic material from the mantle that caused that melting when the compositions of pain of suites from the bega batholith of southeastern australia are compared any differences seen at either end of the range in composition are also seen at the other limit so that both the most mafic and mostfelsic rocks show similar relative abundances of particular elements similar relationships are seen for other granites in the region these observations are not consistent with largescale magma mixing or mingling and although those processes may operate on a small scale they cannot have been responsible for the major compositional variations likewise assimilation of country rocks had no significant role in producing variation in the granites of southeastern australia the production of variation by differential separation of melt from residual solid source material or restite must be favoured for many of the granite suites of this region

the molybdenum isotopic compositions of i s and a type granitic suites this study reports mo isotopic compositions for fifty two palaeozoic granitic rocks with contrasting source affinities a i and s type from the lachlan fold belt lfb and the new england batholith neb both in se australia and three compositionally zoned plutons loch doon criffell and fleet located in the southern uplands of scotland the results show relatively large variations in 98mo for igneous rocks ranging from 1 73 to 0 59 with significant overlaps between different types no relationships between 98mo and 18o or asi alumina saturation index are observed indicating that mo isotopes do not clearly distinguish igneous vs sedimentary source types instead effects of igneous processes source mixing regional geology as well as hydrothermal activity control the mo isotope compositions in these granites it is found that mo is mainly accommodated in biotite and to a lesser extent in hornblende hornblende and fe3 rich minerals may preferentially incorporate light isotopes as reflected by negative correlations between 98mo and k rb and fe2o3 there is a positive correlation between initial 87sr 86sr and 98mo in i type granitic rocks reflecting the admixing of material from isotopically distinct sources granitic rocks from scotland and australia display strikingly similar curvilinear trends in 98mo vs initial 87sr 86sr despite the differing regional geology localized hydrothermal effects can result in low 98mo in granite as seen in three samples from loch doon and criffell which have anomalously light 98mo of 1 based on this study an estimate of 98mo 0 14 0 07 95 s e for the phanerozoic upper crust is proposed this is slightly heavier than basalts indicating an isotopically light lower crust and or a systematic change to the crust resulting from subduction of isotopically light dehydrated slab and or pelagic sediment over time

h type hybrid granitoids a proposed revision of the granite type classification and nomenclature abstract recent studies on calc alkaline plutonic rocks reveal field and petrographic relationships with strong implications for the processes involved in their genesis the presence of magmatic inclusions and magma mingling zones in these rocks supports an origin by magma mixing compositional variations and isotopic anomalies are a good test for such petrogenetic models most of these calc alkaline plutonic rocks which characterize both collision related and active plate margin environments have been classically identified as i igneous type granitoids following chappell and white s 1974 classification and then interpreted as derived from partial melting of older igneous rocks restite model if the magma mixing origin of a type of granitoids can be demonstrated from field and petrographic evidence and supported by chemical and isotopic variations the nomenclature must be changed in this sense the new category of h hybrid type is tentatively introduced it includes most of the so called i type granitoids and some of the s type as deduced from field relationships of magma mingling zones a mixing model is suggested that can operate on a large scale to explain the petrogenesis of the hercynian calc alkaline granodiorites of iberia finally a modified classification of common plutonic rocks in orogenic environments is proposed

cellular plagioclase intergrowths as a result of crystal magma mixing in the proterozoic aland rapakivi batholith sw finland finely cellular plagioclase intergrowths have been studied in xenocrystic andesine an32 and andesine mantled k feldspars within mafic magmatic enclaves in a quartz feldspar porphyry from the proterozoic subvolcanic hammarudda complex aland rapakivi batholith sw finland the cellular intergrowths usually occur as 0 2 2 0 mm mantles around xenocrysts but also as entirely cellular grains and are built up of a network of two distinct phases one relatively na rich an31 and one relatively ca rich an50 the grains are also covered by a thin 0 08 0 12 mm continuous normally zoned rim outside the cellular mantle small inclusions 0 01 0 05 mm of fe mg minerals are concentrated in the ca rich part of the network compositionally the na rich phase of the network is close to the inner non cellular andesine of the xenocrysts however it has a lower or and a slightly lower an content the ca rich phase has the same composition as the inner part of the normally zoned rim which outwards grades into lower an contents that overlap the an content of the matrix plagioclases the cellular network was developed after the andesine xenocrysts or andesine mantled k feldspars were engulfed in mafic magmatic enclaves during a mixing event the xenocrysts became heated to a temperature just below the liquidus of the mafic magma dissolution of the xenocrysts developed a spongy cellular texture which was penetrated by enclave magma ca rich plagioclase crystallized in the cells in equilibrium with the enclave magma trapping fe mg rich melt as the enclaves cooled the outermost thin rim and matrix plagioclases crystallized from the mafic melt these processes operated in fairly large enclaves as the one studied here which has a diameter of 70cm smaller enclaves on the other hand were cooled more rapidly to temperatures close to the solidus of the enclave magma and consequently had no time to dissolve the xenoxrysts

application of the restite model to the deddick granodiorite and its enclaves a reinterpretation of the observations and data of maas et al 1997 mafic s type granites of the lachlan fold belt always contain a introduction distinctive suite of enclaves dominated by schists and gneisses of high maas et al 1997 have proposed complex models of metamorphic grade generally with lesser numbers of microgranular crustal melting and magma mixing to account for the enclaves maas et al 1997 journal of petrology 38 chemical and isotopic features of several kinds of enclaves 815 841 recently described enclaves from the s type deddick in the s type deddick granodiorite of the lachlan fold granodiorite they concluded that the metasedimentary enclaves belt lfb exposed at mckillops bridge that grancould be either source lithologies or accidental xenoliths and that odiorite is a member of the bullenbalong suite area the most common microgranular enclaves formed as globules of 3100 km white chappell 1988 itself part of the hybrid magma that mingled with the host magma all features of very extensive and slightly more diverse bullenbalong the metasedimentary enclaves are consistent with an origin as lithic supersuite total area 8750 km plus 4000 km of restite fragments from the source and their ubiquity in the mafic svolcanic rocks it occurs near the southern extremity of type granites and their rarity in both felsic varieties and in i type those granites these are the rocks that have been used granites conform with such an origin the argument that these as primary examples of restite and of the restite model enclaves are not in chemical equilibrium with the host granite in s type granites hine et al 1976 white chappell because they do not complement its composition is not valid as they 1977 chappell et al 1987 chappell 1996b and the represent less fertile parts of the source that did not melt to the point enclosed enclaves have been regarded by us as lithic of disaggregation unaltered cores of microgranular enclaves in the restite white chappell 1988 chen et al 1989 s type granites have compositions that do not match those of any chappell white 1991 white et al 1991 wyborn known igneous rock and an origin by metamorphism of a calcareous et al 1991 sediment is probable partial melting during that metamorphism maas et al 1997 mostly reject the presence of restite accounts for the pseudo igneous textures seen in these enclaves enclaves in the deddick granodiorite however the

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

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

inherited deformation structures in metasedimentary enclaves in granites as windows into deeper levels of the crust abstract deformation structures preserved in metasedimentary enclaves in granites can provide information on the deformation history of the granite source region up to the time of melt generation particularly where the inclusions record more deformations than were present in the country rock at the time of emplacement the data provide a window to the source that is additional to that derived from petrology and geochemistry the improved view can give extra information about the nature of the source rocks and their structural tectonic history if applied across a wide region such as an orogenic belt the approach could provide fundamental information on large expanses of unexposed crust and could help delineate suspected or unsuspected boundaries between terranes or basement terranes examples from two granitic plutons in the palaeozoic lachlan foldbelt of southeastern australia support independent assertions that at least in places the foldbelt structurally overlies pre ordovician late proterozoic cambrian continental crust rather than oceanic crust alternatively it overlies ordovician continental crust the structural and chemical composition of which are different from ordovician rocks at surface

generation of tonalitic and dioritic magmas by coupled partial melting of gabbroic and metasedimentary rocks within the deep crust of the famatinian magmatic arc argentina the source regions of dioritic and tonalitic magmas have been identified in a deep crustal section of the famatinian arc sierras pampeanas of western argentina the source zones of intermediate igneous rocks are located at the transition between a gabbro dominated mafic unit and a tonalite dominated intermediate unit in the upper levels of the mafic unit mafic magmas intruded into metasedimentary wall rocks crystallized mainly as amphibole gabbronorite and caused the partial melting of the surrounding metasediments in turn the leucogranitic melts sourced from the metasedimentary rocks intruded into the newly crystallized but still hot mafic layers and catalysed the process of partial melting of the gabbroic plutonic rocks the gabbroic rocks became mafic migmatites comprising amphibole rich pyroxene bearing mesosomes and leucotonalitic veins significantly most of the mafic migmatites have isotopic compositions sr sr t 50 7063 and end t 1 4 0 94 to 2 24 similar to those of the gabbroic rocks and distinct from those of their complementary leucotonalitic veins sr sr t 1 4 0 7075 0 7126 and end t 5 2 65 providing evidence for the idea that melting of the mafic rocks was triggered by the intrusion of leucogranitic anatectic melts sr sr t 1 4 0 715 and end t 1 4 6 21 mass balance calculations show that the model reaction plagioclase amphibole leucogranitic melt leucotonalitic melt clinopyroxene orthopyroxene can better explain the partial melting of the gabbroic rocks based on field observations we argue that the coalescence of leucotonalitic veins in the mafic migmatites led to breakdown of the solid matrix to form melt dominated leucotonalitic pools however the leucotonalitic veins that crystallized before leaving behind the mafic migmatitic rock are chemically elemental and isotopic more evolved than the dioritic and tonalitic rocks we envisage that once detached from their source region the leucotonalitic magmas were able to react commingle and mix with entrained fragments of both mafic and metasedimentary rocks this process gave rise to melts that became tonalitic and dioritic magmas this study concludes that the generation of intermediate magmas is a multistage process with three critical steps 1 influx and emplacement of hydrous mafic magmas into a deep crust containing metasedimentary country rocks 2 physically and chemically coupled melting of mafic and metasedimentary rocks leading to the formation of a leucotonalitic vein and dyke system that coalesces to form leucotonalitic or tonalitic magma bodies 3 retrogression of the leucotonalitic magmas by partially assimilating entrained fragments of their mafic and metasedimentary precursors the dimensions of the

the origin and petrologic evolution of the ordovician famatinian puna arc elemental chemistry radiogenic isotopic data and zircon u pb inheritance patterns for the famatinian puna arc suggest that the primary petrogenetic process operating in the arc was mixing between subarc mantle derived gabbroic magmas and metasedimentary materials without a substantial component of lower crustal continental basement rocks this mixing is observable in the fi eld and evident in variations of chemical elemental parameters and isotopic ratios revealing that hybridization coupled with fractionation of magmas took place in the upper 25 km of the crust intermediate and silicic plutonic rocks of the famatinia puna arc formed in a subduction setting where the thermal and material input of mantle derived magmas promoted fusion of fertile metasedimentary rocks and favored mixing of gabbroic and dioritic magmas with crustal granitic melts whole rock geochemical and isotopic data for the famatinian puna magmatic belt as a whole demonstrate that the petrologic model studied in detail in the sierra valle fertil la huerta section has the potential to explain generation of plutonic and volcanic rocks across the early ordovician western gondwanan proto pacifi c margin this example further underscores the signifi cance of passive margin sedimentary accumulations in generating continental arcs ducea email arizona edu ducea m n otamendi j e bergantz g w jianu d and petrescu l 2015 the origin and petrologic evolution of the ordovician famatinian puna arc in decelles p g ducea m n carrapa b and kapp p a eds geodynamics of a cordilleran orogenic system the central andes of argentina and northern chile geological society of america memoir 212 p 125 138 doi 10 1130 2015 1212 07 for permission to copy contact editing geosociety org 2014 the geological society of america all rights reserved on september 24 2014 memoirs gsapubs org downloaded from

extreme mineral scale sr isotope heterogeneity in granites by disequilibrium melting of the crust abstract the broadest ranges of initial sr isotopic ratios 87 sr 86 sr i ever reported within a single igneous rock 2 10 2 are preserved within the late miocene laccolith pluton dyke felsic complex of elba island italy for these units the integration of textural and crystal scale isotope data allows tracing the evolution of the 87 sr 86 sr i of the melt from the emplacement level back to the earliest pre emplacement crystallization stage the rock matrix minerals record the 87 sr 86 sr i composition of the magma at the emplacement level 0 715 0 716 k feldspar megacrysts representing an earlier phase crystallized at depth record a rim to core increase of sr isotopic ratios from values similar to those of the matrix to significantly higher ones 0 719 remarkably biotites hosted within megacrysts representing the first crystallization stage have extreme and contrasting 87 sr 86 sr i values in the different intrusive units biotites within megacrysts from the laccolith record the lowest ratio in the intrusive complex 0 710 while those in the megacrysts from the pluton and associated felsic dyke have the highest 87 sr 86 sr i 0 732 this time transgressive record of isotopic variation in the magma reflects episodic recharge and mixing of magma batches formed by disequilibrium melting of crustal sources that produced melts through different reactions as temperature was increasing the progression from muscovite to biotite dominated fluid absent melting generates melts with increasing 87 sr 86 sr while at higher temperatures the progression from biotite to hornblende dominated melting reactions results in a decrease in the 87 sr 86 sr of the melt

evolution of mantle derived augite hypersthene granodiorites by crystal liquid fractionation barrington tops batholith eastern australia the barrington tops batholith btb is a shallow level intrusive complex of permian age 262 ma in zone a of the new england fold belt northern new south wales it comprises a comagmatic suite of early pyroxene plagioclase phyric quartz diorite stocks and dykes 10 by area augite hypersthene granodiorite 75 and aplite less voluminous hornblende biotite granodiorite 15 appears to be related to the augite hypersthene granodiorite by the addition of minor amounts of an incompatible element rich component the augite hypersthene granodiorite plutons formed by fractional crystallisation of a dry 2 0 high temperature 1000 c liquid major element modelling using analysed phenocryst compositions closely reproduces the geochemical differentiation trends observed combined petrographic and mineral chemistry evidence indicates that parental liquids were of quartz dioritic and more mafic compositions probably mantle derived low initial 87 sr 86 sr 0 7036 0 7039 and high nd values 5 6 to 7 8 suggest these were produced from a geochemically depleted mantle source the btb may be regarded as an end member of the spectrum of calc alkaline granitic rocks that are formed by the mixing of variably fractionated melts of upper mantle origin with lower continental crust material it is suggested that lower crustal mafic and ultramafic xenoliths found m mesozoic to cenozoic basalts represent cumulates complementary to the more evolved mantle derived component of calc alkaline magmatism crystal liquid fractionation aided by mixing of evolved mantle derived magma with crustal material appears to be the most important process giving rise to the diverse geochemical and isotopic continuum displayed by calc alkaline magmatism m orogemc terrains

the genesis of felsic mafic plutonic associations a sr and nd isotopic study of the hercynian braga granitoid massif northern portugal abstract the late tectonic braga plutonic complex in the centro iberian zone north portugal was emplaced during the hercynian orogeny within a silurian sedimentary sequence and displays an acid basic association which consists of three well defined intrusions the biotite dominant braga granite minor bodies of gabbro to granodiorite composition and the mildly peraluminous gonca leucogranite these three plutonic suites present field relationships indicating a synchronous magmatic emplacement for which a rb sr age of 310 10 ma is obtained the distribution of the three plutonic units along regular curves in major and trace element diagrams suggests that the different units can be genetically related however the rb sr and sm nd isotopic results do not indicate a unique homogeneous source and a simple fractional crystallization process the gabbros have chemical characters high k ba sr and light rare earth elements and low nb ti and zr contents and isotopic compositions sri 0 70497 and nd 2 5 which suggest an alkaline magmatic affinity of shoshonitic type they are probably derived from an enriched mantle source in contrast the peraluminous gonca leucogranite sri 0 70933 and nd 6 8 is more likely the result of crustal anatexis the braga granite and the evolved members of the basic series have an intermediate isotopic composition sri 0 70532 to 0 70733 and nd 3 0 to 6 2 which can be interpreted in terms of an hybridization process between the two previous end members the chemical and sr nd isotopic compositions of the braga plutonic series can be explained by an assimilation fractional crystallization afc model between a mantle derived magma equivalent to the gabbros and a crust derived magma the gonca granite

the two component model for the genesis of granitic rocks in southeastern australia nature of the metasedimentary derived and basaltic end members granitic magmas in three areas of southeastern australia are the product of melting of quartzofeldspathic metasedimentary rock high silica end member combined with varying degrees of incorporation of mafic dominantly basaltic magma low silica end member the link between granitic magma and local metasedimentary rock is established by identifying shared geochemical signatures in sr na2o and k2o contents high silica end members have compositions formed in a genetic spectrum from total source mobilisation to partial melt segregation from metasedimentary rock the position of a granitic end member in this spectrum is monitored by titanium contents varying from normal metasedimentary to the strongly depleted induced by partial melting the titanium signature of partial melting is established in a type area with unequivocal links between migmatite mesosomes and leucosomes and the high silica end members of granitic variation systems that extend to lower silica the low silica end members approximate high alumina basalts on the basis of observed gabbros and projection of granitic variation lines to equivalent gabbroic compositions high alumina basalt is postulated to be a fundamental ingredient in the petrogenesis of orogenic granitic rocks

late archaean crust mantle interactions geochemistry of lree enriched mantle derived magmas example of the closepet batholith southern india the closepet batholith in south india is generally considered as a typical crustal granite emplaced 2 5 ga ago and derived through partial melting of the surrounding peninsular gneisses 3 3 to 3 0 ga in the field it appears as a composite batholith made up of at least two groups of intrusions a an early sio2 poor group clinopyroxene quartz monzonite and porphyritic phyritic monzogranite is located in the central part of the batholith these rocks display a narrow range in both initial 87sr 86sr 0 7017 0 7035 and nd 0 9to 4 1 b a later sio2 rich group equigranular grey and pink granites is located along the interface between the sio2 poor group and the peninsular gneisses they progressively grade into migmatised peninsular gneisses thus indicating their anatectic derivation their isotopic characteristics vary over a wide range 87sr 86sr ratios 0 7028 0 7336 and nd values from 2 7 to 8 3 at 2 52 ga field and geochronological evidence shows that the two groups are broadly contemporaneous 2 518 2 513 ga and mechanically mixed this observation is supported by the chemical data that display well defined mixing trends in the sr vs nd and elemental variation diagrams the continuous chemical variation of the two magmatic bodies is interpreted in terms of interaction and mixing of two unrelated end members derived from different source regions enriched peridotitic mantle and peninsular gneisses it is proposed that the intrusion of mantle derived magmas into mid crustal levels occurred along a transcurrent shear zone these magmas supplied additional heat and fluids that initiated anatexis of the surrounding crust during this event large scale mixing occurred between mantle and crustal melts thus generating the composite closepet batholith the mantle derived magmatism is clearly associated with granulite facies metamorphism 2 51 0 01 ga ago both are interpreted as resulting from a major crustal accretion event possibly related to mantle plume activity

a reappraisal of the evolution of the palaeo pacific margin of gondwana from the pb and os isotope systematics of igneous rocks from the southern adelaide fold belt south australia abstract we have undertaken pb and os isotopic analyses of igneous rocks from the southern adelaide fold belt to further understanding of the neoproterozoic early palaeozoic evolution of the palaeo pacific margin of gondwana the new pb isotope data and a reappraisal of existing geochronological data suggest that layered mafic intrusions at black hill and cambrai may have intruded much earlier than previously thought intrusion may even have occurred prior to deposition of the normanville and kanmantoo group sediments and the onset of what is traditionally regarded as the delamerian orogeny we tentatively term this earlier event the hallett cove orogeny however equivalent ages are common in the formerly adjacent ross orogen when the pb isotope signatures of the suites of gabbros and i s and a type granites are compared at 487 ma they all span a very large range 206pb 204pbi 15 4 18 7 207pb 204pbi 15 4 15 7 208pb 204pbi 33 0 38 8 compared with other formerly adjacent terranes or the subsequent lachlan fold belt similarly 187os 188osi ratios span 0 122 1 17 but include one gabbro and one rhyolite that have subchondritic 187os 188osi ratios when taken together the combined data do not support models in which the observed range in initial isotope ratios reflects major and variable mid to upper crustal assimilation of magmas derived from the contemporary asthenospheric mantle rather it appears that magmas parental to the gabbros and a type rocks were derived from subduction modified lithospheric mantle that has a median metasomatic age of 1 4 ga large scale pb isotopic homogenization as proposed for the lachlan fold belt did not occur in the adelaide fold belt

evolution of the nw margin of the north permian basin uk north sea mapping of depositional zones within the zechstein supergroup using semi regional 2d and 3dseismic data constrains the geological evolution of the northwestern margin of the north permian basinin uk offshore quadrants 14 15 19 20 and 21 four depositional zones are identified on the basis of mappable seismic facies which are assumed to vary with halite content well control characterizes the most reflective seismic facies as an interbedded carbonate and anhydrite shelf succession which grades laterally through clastic rich sequences to the least reflective a thick halite basinal equivalent the trendsof the depositional zones illustrate the geometry of the north permian basin and may have been locally controlled by basement lineaments within the north permian basin a n s trending axis devil s hole high characterized by thick reflective facies separates the central north sea from the forth approaches basin basement fault blocks control facies type and thickness along the northwest margin of the north permian basin in the moray firth area permian tilt of the zechstein shelf related to regional flexure played a role in precipitating gravity driven tectonics within the seismically reflective facies on the east flank of the devil s hole high this permian phase of salt tectonics resulted in numerous intra zechstein structures which can be interpreted as rafted and folded zones of interbedded halite carbonate sulphate and clastics the rafts initially slid downdip towards the main halite basin then their evolution became dominated by differential subsidence of the interbeds which forced salt layers into adjacent passive diapirs this episode predates deposition of the triassic smith bank shales which rest upon the zechstein with local angular unconformity the spatial distribution of zechstein facies influenced the tectonostratigraphy of the triassic jurassic and cretaceous systems boundaries between zechstein facies correspond to the limit of triassic halokinesis on the west central shelf and the limit of detachment of jurassic and lower cretaceous thin skinned tectonics in moray firth half graben

recycling of orogenic arc crust triggers porphyry cu mineralization in kerman cenozoic arc rocks southeastern iran pre collisional eocene oligocene arc diorites quartzdiorites granodiorites and volcanic equivalents in the kerman arc segment in central iran lack porphyry cu mineralization and ore deposits whereas collisional middle late miocene adakite like porphyritic granodiorites without volcanic equivalents host some of the world s largest cu ore deposits petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment ore hosting kuh panj porphyry intrusions exhibit high sr 400 ppm low y 20 no negative eu anomalies eu eu 1 and relatively non radiogenic sr isotope signatures 87sr 86sr 0 7042 0 7047 relative to eocene oligocene granitoids mainly sr 12 la yb 15 eu eu 1 87sr 86sr 0 7053 0 7068 trace element modeling indicates peridotite melting for the barren eocene oligocene intrusions and a hydrous garnet bearing amphibolite source for middle late miocene ore hosting intrusions the presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30 35 to 40 45 km or 12 kbar the changes in residual mineralogy in the source of eocene to miocene rocks in the kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel underplating of cu and sulfur rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust mantle boundary and dehydration melting under oxidizing conditions produced syn and post collisional ore hosting intrusions while the lack of post collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur rich and oxidized adakitic magmas

repeated s i a type granite trilogy in the lachlan orogen and geochemical contrasts with a type granites in nigeria implications for petrogenesis and tectonic discrimination

o sr isotopic variations in miocene granitoids from the aegean evidence for an origin by combined assimilation and fractional crystallization sr o and d h isotopic compositions have been analyzed in miocene metaluminous to slightly peraluminous i type granitoids of the central aegean individual plutonic complexes display significant variations in their 18o and initial87sr 86sr compositions d and 18o compositions of minerals and whole rocks are mostly in the magmatic range some samples from naxos and mykonos delos show low d and 18o values characteristic of meteoric water hydrothermal interaction but as a whole the changes in 18o and sr isotopic compositions as a result of hydrothermal alteration were slight even in instances where marked alteration is petrographically observable consequently the bulk rock variations of 18o from 8 1 to 12 0 and of87sr 86sr from 0 70438 to 0 71450 may be regarded as primary and indicative of the conditions of their evolution heterogeneous isotopic compositions observed in the individual plutons of serifos ikaria samos and kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization the granitoids of serifos ikaria and kos display weak correlations between the initial87sr 86sr and 18o and 1 sr the granitoid province shows a positive correlation between87sr 86sr and 18o and a non linear relationship between87sr 86sr and 1 sr whereby 1 sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases it is argued that assimilation of older continental material by mantle derived arc magmas with combined fractionation afc is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock types trend from granodiorites in the south west near the inferred oligocene miocene suture to granites in the center and monzonites in the north east of the province

petrogenesis of granitoids from the lachlan fold belt southeastern australia the role of disequilibrium melting abstract s and i type granites from the lachlan fold belt southeastern australia have been investigated to assess the role of disequilibrium melting in their petrogenesis differences between the median initial ehf compositions of magmatic zircon populations and the host bulk rock ehfblk zrc range from 0 6 to 2 5 e units providing evidence for intra sample and hence inter phase hf isotopic heterogeneity linear variations on harker diagrams and o and hf isotope compositions of magmatic zircon preserved in many i and s type granites are inconsistent with assimilation or simple mixing hypotheses in contrast isotopic disequilibrium between the melt and a restite assemblage can explain the bulk rock versus zircon differences observed in these samples assuming that magmatic zircon records the melt composition differences between the bulk rock ehf and ehf of magmatic zircon ehfblk zrc values measured for i type granites 0 4 2 5 can largely be explained by disequilibrium amphibole dehydration melting of meta igneous protoliths that were either isotopically heterogenous at the time they were formed or perfectly homogeneous before being aged in the crust for 0 4 1 0 billion years prior to partial melting the currowong suite exhibits petrographic features and preserves geochemical and isotopic compositions that do not lend themselves to simple restite model or magma mixing explanations however these observations could be explained by the restite unmixing of magma batches generated from a single source rock if as modelling has suggested separate batches contain different melt compositions by investigating the application of disequilibrium melting to granite genesis this study demonstrates that isotopic heterogeneity at various sampling scales should actually be expected for the production of granites from a single source rather than necessitating the involvement of multiple sources and mixing processes as a result great care should be taken in the interpretation of isotope data from granitic bulk rocks or their zircons

analytical determination of nearshore wave height variation due to refraction shoaling and friction abstract explicit wave formulae derived from the dispersion relation for linear waves are used to find an analytical solution to the problem of wave height variation on a simple topography i e topographies with incrementally constant slope and straight parallel contours the solution accounts for shoaling refraction and frictional dissipation and will be sufficiently accurate for practical purposes considering the simplifying assumptions that are necessary for treatment of this problem by any method the solution is simple enough to be handled on a personal calculator and has the advantage over numerical solutions that it can be solved for other parameters for example to give friction factors from observed wave height data the last chapter contains updated formulae for wave friction factors over movable beds

the silicon isotope composition of granites because weathering results in preferential incorporation of the lighter si isotopes into clay minerals the si in magmas derived from meta sedimentary lithologies enriched in such phases should also be isotopically light relative to melts derived from igneous sources with the advent of new high precision techniques it should therefore be possible to resolve such differences hence si isotopes have to potential to distinguish between and characterise different magmatic source regions to explore this here we report the si isotopic compositions of a suite of phanerozoic i s and a type granites and mineral separates as well as samples of associated country rock the whole rock data fall between 30si 0 40 and 0 11 0 04 95 s e this range is more limited than that defined by previous low precision measurements of granites but is significantly broader than that displayed by more recent high precision measurements of high si extrusive igneous rocks as predicted s type granites are on average isotopically lighter than i and a type samples and negative correlations with alumina saturation index asi values and initial 87sr 86sr provide evidence that si isotope variations in granites can be explained by variable incorporation of an enriched sedimentary component however the relatively small isotopic perturbations and apparent degree of overlap between granite affinities suggest that si isotopes are not as sensitive to sedimentary input relative to more established proxies such as for example o isotopes the average si isotope value of all granites analysed in this study is 30si 0 23 0 15 2 s d which is entirely consistent with a recently published estimate for the continental crust based on an andesitic bulk composition and the well defined relationship between si isotopes and magmatic fractionation

an example of trondhjemite genesis by means of alkali metasomatism rockford granite alabama appalachians a model for trondhjemite genesis is proposed where granite is transformed to trondhjemite via infiltration by a na rich metamorphic fluid the rockford granite of the northern alabama piedmont serves as the case example for this process and is characterized as a synmetamorphic peraluminous trondhjemite granite suite the major process operative in the conversion of granite to trondhjemite involves cation exchange of na for k in the feldspar and mica phases through a volatile fluid medium whole rock 18o values for the trondhjemites are negatively correlated with atomic proportion k na ratio indicating a partial reequilibration of the altered granitoids with a na and18o rich metamorphically derived fluid biotite decomposition to an al epidote paragonitic muscovite secondary quartz assemblage is also associated with the sodium metasomatism as are apatite replacement by al epidote and secondary zircon crystallization rare albitization of primary magmatic plagioclase and discontinuous grossularite reaction rim growth on magmatic garnet are present in the trondhjemites indicating the mobility of ca during alkali metasomatism the replacement of magmatic phases by me tasomatic phases exemplifies the chemical changes produced during infiltration metasomatism where the trondhjemites are depleted in p2o5 th rb u k2o v sn f mgo pb tio2 feo and li and enriched in cao na2o zr and sr relative to the granites other elements such as cr mno cu zn co ba sio2 ni al2o3 are shown to be relatively immobile during the metasomatism the infiltration metasomatism probably occurred during prograde regional metamorphism when a discrete fluid phase was produced in the surrounding amphibolite grade metasediments foliation planes in the granite apparently served as conduits for fluid flow with reaction enhanced permeability accompanying the 8 molar volume reduction during na for k exchange in the feldspars a source for the na and sr in the metamorphic fluid may have been paragonitic muscovite in the metasedimentary country rocks rubidium and k were probably retained in metasedimentary biotite the silent lake pluton in southeastern ontario is a possible analogue to the alkali metasomatic processes affecting the rockford granite

isotopic evidence for rapid continental growth in an extensional accretionary orogen the tasmanides eastern australia the trace element signature of earth s continental crust resembles that of arc lavas but the continents may have formed during ancient igneous pulses that are hard to reconcile with supra subduction zone magmatism we explore the role of coupled arc back arc accretionary processes in crust generation by considering the tectonic context of whole rock nd isotope and zircon hf o isotope data from igneous rocks of the australian tasmanides 515 230 ma which is thought to have evolved by the repeated opening and closure of sediment filled back arc basins behind a long lived subduction zone the significance of this process for continental crust formation has yet to be evaluated from an isotopic perspective granitic rocks in this area define striking secular end ehf 18o trends that correlate with the pattern of deformational events and register changes in magma source during tectonic activity these trends reveal that juvenile magmatic input was enhanced during extensional back arc rifting episodes that immediately followed crustal thickening suggesting a relationship between slab rollback and continental growth interaction between juvenile magma and sedimentary units deposited during a preceding back arc rifting cycle was integral to the formation of stable continental material this highlights the importance of back arc environments for both the generation and differentiation of continental crust the juvenile component within the tasmanide igneous rocks increased from the cambrian to the triassic consistent with a diminished input from cratonderived metasedimentary material as the subduction zone migrated outboard of the gondwana margin subduction zone retreat formed large tracts of new crust in eastern australia at comparable rates to crust generation at modern island arcs providing a mechanism for rapid continental growth at convergent margins using isotopic tracers to link tectonic evolution and crust generation in modern and ancient orogens can lead to a better understanding of the geodynamic controls on planetary differentiation