a garnet two mica granite coyote mountains southern arizona geologic setting uranium lead isotopic systematics of zircon and nature of the granite source region the 58 m y old pan tak granite considered representative of the widespread early tertiary garnet two mica granites of south central arizona consists of biotite and muscovite biotite granite intruded by garnet muscovite and garnet biotite granite and associated pegmatite textural evidence indicates that muscovite is a primary magmatic mineral the granite was intruded into jurassic dioritic to granitic rocks and paleozoic metasedimentary rocks during a latest cretaceous and early tertiary regional metamorphic episode part of the pluton was subsequently mylonitized during an early or middle tertiary deformational episode of metamorphic core complex aspect the fabrics produced by these two metamorphic episodes differ in distribution style orientation and probably age the zircon population of the pan tak granite consists of a mixture of small euhedral crystals and larger rounded crystals with or without overgrowths uranium lead isotopic ratios of five size fractions of discordant zircon define a chord with a lower concordia intercept age of 58 2 m y and a late precambrian upper intercept 207 pb 206 pb ages range from 214 m y for the finest fraction to 434 m y for the coarsest fraction the pan tak discordia is interpreted as a mixing line between 58 m y old magmatic zircon and an older zircon component largely or entirely of late precambrian age geologic and isotopic evidence indicates that this older zircon component was not assimilated from the country rocks but rather was inherited from the source material of the granite the presence of this inherited zircon indicates that the pan tak magma was produced by melting of crustal rocks containing late precambrian zircon this source material was probably the 1 7 to 1 4 b y old crystalline basement of south central arizona generation of the pan tak and related granites by crustal anatexis was one aspect of a latest cretaceous to early tertiary orogenic episode in south central arizona

origin of mesozoic and tertiary granite in the western united states and implications for pre mesozoic crustal structure 2 nd and sr isotopic studies of unmineralized and cu and mo mineralized granite in the precambrian craton in the cordilleran region of the western united states mesozoic and tertiary peraluminous granitic rocks display regional variations in initial 143nd 144nd end end 10 to 12 in southern arizona 17 to 19 in the northern great basin ngb and 30 in the northern rocky mountains initial 87sr 86sr values are between 0 710 and 0 721 and show no regional pattern metaluminous granitic rocks have a wider range of end values extending from values similar to those of the peraluminous granites to much higher values the 87sr 86sr values are mostly fairly low between 0 705 and 0 710 except in the ngb where values as high as 0 7157 are observed no systematic differences between the end or 87sr 86sr values of cu or mo mineralized and unmineralized granite were discerned except for cu mineralized granite in eastern nevada and mo mineralized granite in colorado which have end values higher 0 and lower 10 0 respectively than unmineralized granite in the same region comparison to end values of exposed precambrian rock suggests that the peraluminous granite and the mo granite in colorado were derived exclusively from felsic precambrian basement rocks and that the regional variations in the end values reflect the regional variation in the average crustal age the nd data confirm that the precambrian basement underlying the ngb and eastern california is isotopically distinct from precambrian crust in the remainder of the western united states the similarity between the end values of peraluminous granite and precambrian crust also suggests that the high 147sm 144nd 0 13 and the low total light rare earth element lree abundances characteristic of peraluminous granite in southern arizona were imposed during the chemical evolution of the magmas metaluminous granite are interpreted to have formed via mixing of mantle derived magma and large proportions of low 87sr 86sr granulite facies lower crust except in the eastern ngb where the mantle magmas mixed with a lower crustal source with a significantly higher 87sr 86sr ratio ree abundance patterns for metaluminous granite in the ngb are characterized by extreme lree enrichment which supports the proposed origin for these rocks by mantle crust mixing or by remelting of the lower crust alone no systematic difference exists between the sources of cu or mo mineralized and unmineralized metaluminous granite but the data suggest that the cu sources are in the mantle and the mo sources are in preexisting crust overall the nd data indicate that continental interior granite in the western united states was primarily derived from preexisting crust and although changes in the thermal structure of the continental mantle may have triggered magma formation the resulting granites do not represent significant juvenile additions to the continental crust

spatial and temporal relationships between mid tertiary magmatism and extension in southwestern arizona cenozoic magmatism in southwestern arizona which is within the basin and range tectonic province occurred almost entirely between 15 and 25 ma volcanic rocks typically consist in ascending order of 1 a thin sequence of mafic to intermediate lava flows 2 voluminous felsic lava flows and pyroclastic rocks with minor to moderate amounts of intermediate to mafic lava flows and 3 basalt and andesite volcanic rock sequences rest disconformably on pre tertiary bedrock in most areas but locally overlie substantial coarse clastic debris that was deposited immediately before and during earliest magmatism prevolcanic clastic debris is interpreted as a consequence of local early normal faulting in most regions tilting related to extension began later and occurred during or after eruption of felsic volcanic rocks and before the end of younger mafic volcanism extension generally ended before about 17 ma except in a northwest trending belt adjacent to the relatively unfaulted and topographically elevated transition zone tectonic province which is adjacent to the colorado plateau rapid cooling of metamorphic core complexes and tilting of young basalts and coarse clastic rocks continued in this belt until as recently as 11 ma extension was extreme in this belt whereas it was generally moderate to slight in other parts of southwestern arizona large magnitude extension was not associated with areas of greatest igneous activity and rapid cooling and exhumation of core complexes postdated local magmatism these relationships are inconsistent with theories that relate genesis of metamorphic core complexes to magma intrusion in the upper crust except for young extension in this northwest trending belt there are no apparent regional migration trends for either magmatism or extension within southwestern arizona lack of substantial extension before magmatism and general lack of magmatism during youngest extension are inconsistent with the hypothesis that magmatism was the product of decompression melting during lithospheric extension the long duration and large magnitude of extension adjacent to the transition zone tectonic province and within an area of earlier crustal thickening are consistent with the hypothesis that extension was driven by the gravitational potential energy of elevated land mass and crustal roots regional magmatic heating apparently weakened the lithosphere and triggered extension but did not control extension locally

nd isotope systematics of coarse and fine grained sediments examples from the middle proterozoic belt purcell supergroup sm nd isotopic compositions are reported for 20 fine and 5 coarse grained samples of the belt purcell supergroup of western north america varepsilon nd and sm nd ratios for fine grained belt purcell sediments are remarkably uniform indicating crustal residence ages ranging only from 1 6 to 2 1 ga varepsilon nd and sm nd ratios for coarse grained sediments however are much more varied and contain evidence of sm nd fractionation during sedimentary recycling assuming that this ree fractionation occurred between the time source areas were eroded and when sediment was deposited a new method of calculating crustal residence age intervals is derived for the coarse grained samples which serves to place constraints on the average time since source materials were extracted from the mantle the nd data from both sample groups provide an average age estimate of 2 0 pm 0 3 ga for the middle proterozoic crust from which most of the belt purcell supergroup was derived the isotopic data toge

san jacinto intrusive complex 2 geochemistry rocks from three large 100 2 km tonalitic intrusions exposed in the san jacinto mountains of southern california show a restricted compositional range of between 63 and 68 wt sio 2 for all but volumetrically minor felsic differentiates with si0 2 70 wt all rocks with less than 65 5 wt sio 2 show linear element element covariation felsic differentiates have characteristics higher sio 2 k 2o rb ba u higher and variable rare earth elements consistent with derivation by in situ fractionation rocks with between 65 5 and 70 wt sio 2 have intermediate characteristics and are interpreted as derived from liquids formed by mixing primitive liquids with fractionated liquids within an intermittently recharged continuously solidifying magma chamber mafic inclusions extend the compositional trends of the mafic tonalites to 55 wt sio 2 the chemical variations of both inclusions and more mafic tonalites are interpreted as resulting from processes acting before injection of their parental liquids into the observed crustal magma chambers effects of chamber processes are minor for all but the most felsic rocks the major effect of recharge is to buffer the thermal and chemical properties of liquids within the magma chambers yielding large volumes of relatively homogeneous tonalite for those elements where the bulk distribution coefficient is between about 0 5 and 2 concurrent recharge and solidification produces rocks that closely approximate the composition of the added liquids estimated rayleigh numbers for these liquids are high 10 10 implying convection throughout much of the solidification history of each chamber existence of trace element variations within analyzed rocks imply that convection was not totally efficient at homogenizing the various batches of liquid added to each chamber

depletion of light rare earth elements in felsic magmas contrary to simple generalizations about their behavior light rare earth elements lree do not act as incompatible elements in very felsic magmas in fact lree concentrations typically decrease often drastically during differentiation of such magmas the simplest explanation for this depletion involves the separation of minute easily overlooked quantities of an extremely lree rich accessory mineral either monazite or allanite our data indicate that felsic liquids with 50 ppm lree may be saturated in either of these accessories and that the concentration required for saturation decreases in increasingly felsic liquids this accounts for incompatible behavior of lree even at high concentrations in mafic magmas in contrast to compatible behavior at low concentrations in felsic magmas partitioning of lree into solid rather than liquid has important implications for trace element and nd isotope modeling of crustal anatexis as well as for magma differentiation

influence of tides on melting and freezing beneath filchner ronne ice shelf antarctica an isopycnic coordinate ocean circulation model is applied to the ocean cavity beneath filchner ronne ice shelf investigating the role of tides on sub ice shelf circulation and ice shelf basal mass balance including tidal forcing causes a significant intensification in the sub ice shelf circulation with an increase in melting 3 fold and refreezing 6 fold the net melt rate and seawater flux through the cavity approximately doubles with tidal forcing the spatial pattern and magnitude of basal melting and freezing generally match observations the 0 22 m a 1 net melt rate is close to satellite derived estimates and at the lower end of oceanographic values the ice shelf water outflow mixes with shelf waters forming a cold 1 9 degrees c dense overflow 0 83 sv that spills down the continental slope these results demonstrate that tidal forcing is fundamental to both ice shelf ocean interactions and deep water formation in the southern weddell sea citation makinson k p r holland a jenkins k w nicholls and d m holland 2011 influence of tides on melting and freezing beneath filchner ronne ice shelf antarctica geophys res lett 38 l06601 doi 10 1029 2010gl046462

tectonic evolution of sw wales during the upper palaeozoic during the upper palaeozoic the development of several strike faults strongly influenced the deformation history of sw wales this aspect of the deformation is emphasized in this new description of the tectonic evolution of the region after the caledonian orogeny several strike faults caused crustal extension by normal dip slip and partially controlled the subsidence of depositional basins these faults ceased moving before the initiation of variscan deformation in sw wales two of the earlier faults were reactivated with reverse slip translations during variscan deformation when three strike faults were initiated as a result of gravitational spreading two of the new faults formed sole thrusts for northward translating nappes and the other developed as a subsidiary lag fault the sole thrusts transected some of the pre existing faults causing along strike variation in their motion the strike faults in sw wales were therefore initiated at different times and display contrasting displacement histories

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

a balanced section across the pyrenean orogenic belt evolutionary models that have been proposed for the pyrenean orogenic belt involve gravitational gliding of major thrust sheets to both the north and south of an uplifted central axial zone it has been suggested by previous workers that uplift is a result of alpine compression or long lived strike slip movement on the north pyrenean fault we critically assess these models and propose a new model based on the generation of a thin skinned linked thrust system due to alpine collision of iberia and europe pyrenean alpine tectonics is dominated by southward thrusting on a major sole fault dipping north at approximately 6 within hercynian basement northerly directed thrusts of the north pyrenean zone and northern folded foreland are backthrusts from this sole fault a total orogenic shortening of 106 km in the central pyrenees was achieved between the palaeocene and oligocene at a time averaged rate of 0 62 cm yr 1 a thin skinned model requires that the north pyrenean fault is truncated by both northward and southward moving thrusts and occurs in the footwall of the sole fault some 60km north of its present surface trace

geochronology and zircon hf isotope geochemistry of granites in the giant chalukou mo deposit ne china implications for tectonic setting abstract in this contribution the largest porphyry mo deposit in ne china chalukou is selected to provide insights into the tectonic evolution of ne china the deposit was considered to be rift related or climax type porphyry mo deposit developed in an extensional setting while other researchers attributed its formation to the subduction of the paleo pacific ocean in view of different granite petrogenesis between rift type and subduction type porphyry mo deposits geochronological and zircon lu hf isotope studies have been carried out on granitic rocks associated with the chalukou deposit zircon grains from the ore host monzogranite and ore causative granite porphyry yield weighted mean 206pb 238u ages of 166 2 ma and 152 2 ma with molybdenite samples yielding a re os isochron age of 150 2 ma indicating a jurassic age for both granitic intrusion and mo mineralization zircon ehf t values of monzogranite and granite porphyry range from 0 9 to 3 0 and from 1 4 to 0 5 respectively when integrated with published zircon lu hf isotopic data our data suggest that the barren granites both pre and post ore were mainly derived from mantle derived juvenile rocks whereas the syn ore granite requires additional involvement of old continental crust thus a contribution of continental crust to mo mineralization is suggested the petrogenesis and geochemical data reveal that the chalukou deposit is a subduction related porphyry mo deposits and not rift related integrated evidence links its formation to the southeastward subduction of the mongol okhotsk ocean instead of the westward subduction of the paleo pacific ocean

the role of magmatic sulfides and mafic alkaline magmas in the bingham and tintic mining districts utah this paper reports the existence of abundant magmatic sulfides in introduction latite lava vitrophyres and vent facies dikes from the bingham and the eruption of sulfur rich magmas from el chichon tintic districts in central utah these dikes and flows appear to luhr et al 1984 and mt pinatubo westrich gerlach be comagmatic with the ore related monzonite intrusions in addition 1992 in recent years has attracted attention to the limited analytical data suggest that the magmatic sulfides contain most of solubility of sulfur in intermediate magmas and the factors the cu and ag present in the latites magmatic sulfides are preserved potentially responsible for the formation of magmatic only in the least oxidized and least degassed lavas and vitrophyres sulfides and anhydrite however the occurrence of magpetrography of comagmatic dikes and intrusions suggests that matic sulfides in intermediate magmas is not universal resorption and oxidation s degassing of the globules may make many volcanic suites appear to be sulfide unsaturated the metal content available to a magmatic ore fluid minette and inasmuch as magmatic sulfides may sequester chalcophile shoshonite lavas occur in subordinate amounts in the latitic volcanic metals what would their presence signify in magmatic fields associated with latite monzonite intrusions and hydrothermal systems that formed porphyry cu and mesothermal vein ore deposits of the tintic ag pb zn cu au and bingham deposits do they sequester a significant portion of the porphyry cu au mo districts utah the ages chemical and magmatic cu pb zn ag and au thereby restricting modal compositions and field relations of the mafic alkaline lavas metal availability of subsequent ore forming fluids suggest that such magmas mixed and fractionated at shallow crustal we have examined the volcanic rocks from the tintic levels to form the ore related latites and monzonites the unaltered and bingham mining districts fig 1 utah and found mafic alkaline lavas in these districts are some of the most cu rich that almost all of the volcanic units contain magmatic lavas in the great basin province sulfides some quenched dikes and intrusion margins also have preserved magmatic sulfides comparable with those in the volcanic rocks several lines of evidence indicate that the volcanic and intrusive rocks are comagmatic keith et al 1989 1991 waite 1996 the tintic district and east tintic sub district in utah have recorded over

geology geochemistry and tectonic settings of the molybdenum deposits in south china a review abstract south china block scb is the area including the yangtze craton and the huanan orogen where scattered precambrian terranes are usually regarded as segments of cathaysia land it is the third most important molybdenum metallogenic province in china next to the qinling dabie area and northeast china containing 29 mo only or mo dominated 9 w mo sn bi and 8 cu mo deposits these 46 deposits are located mainly in 1 the lower yangtze river belt of the northeastern yangtze craton 2 the northern jiangnan orogenic belt that is generally considered a meso neoproterozoic magmatic arc complex accreted onto the southeastern margin of the yangtze craton 3 the wuyi yunkai orogenic belt characterized by local exposures of proterozoic metamorphic terranes and the more widespread sinian uppermost proterozoic to triassic sedimentary sequences and 4 the southeast coastal volcanic belt characterized by yanshanian andesitic to felsic volcanic rocks their genetic types are dominated by porphyry and skarn mineral systems with only a few quartz vein systems the orebodies form veins lens cylindrical shapes pipes or irregular in shape usually controlled by faults at various scales and volcanic subvolcanic complexes the host rocks are variable in lithologies including granites porphyries volcanic breccias and tuffs clastic sediments and carbonate rocks but the high grade orebodies are usually hosted in carbonate shale sequences hydrothermal mineralization processes can be generally divided into four stages from early to late they are 1 k feldspar quartz veins or veinlets 2 quartz molybdenite stockworks 3 quartz polymetallic sulfide stockworks and 4 quartz carbonate fluorite veinlets fluid rock interaction as exemplified by wallrock alteration evolved from k silicate alteration k feldspar quartz mica through phyllic quartz sericite chlorite epidote to propylitic or argillic alteration with skarn alteration typically occurring in skarn type mineral systems hydrothermal mineral assemblages vary between two end members namely the dry system formed by co2 rich fluids and marked by quartz k feldspar fluorite carbonate and epidote and the wet system mainly originated from co2 poor fluids and composed of biotite sericite and chlorite the ore forming fluids are magmatic in origin and show high temperature and high salinity the melt fluid systems forming cu mo deposits are more oxidizing than those forming the w mo or mo deposits as suggested by accessory minerals in granitoids and daughter minerals in fluid inclusions the cu mo deposits are related to the i type granitic rocks adakite like whereas the w mo and mo only systems are related to granitic rocks of s or a types although all of them show high k contents available isotope ages show that the mo and mo bearing deposits were predominantly formed in the early yanshanian orogeny 170 134 ma followed by the late yanshanian orogeny 110 92 ma and the caledonian orogeny 450 410 ma the caledonian mo mineralization has been observed only in the wuyi yunkai orogenic belt and related to the collision between the yangtze craton and the pre devonian huanan orogen or terranes separated from the cathaysia land linked to the assembly of the gondwana supercontinent the early yanshanian mineralization affected the entire huanan orogen and the eastern yangtze craton and resulted from the syn to post collisional tectonism following the closure of eastern paleo tethys the late yanshanian mo deposits mainly occur in the southeast coastal volcanic belt and the southeastern margin of the wuyi yunkai orogenic belt and are related to the westward subduction of the paleo pacific plate the skarn type mineral systems generally show lower re contents than the porphyry type deposits in a same tectonic unit suggesting that carbonate host rocks have lower re contents than the causative porphyries the re contents in molybdenites from porphyry or porphyry skarn cu mo systems are 50 ppm mainly 100 ppm suggesting a source significantly contributed by the mantle whereas the re contents in molybdenites from the mo only or w mo dominated deposits are

nature and origin of proterozoic a type granitic magmatism in the southwestern united states of america the mountain ranges of arizona and adjacent california and nevada contain large areas underlain by proterozoic anorogenic granites comprising the southwesternmost portion of a transcontinental belt of 1 4 1 5 ga old anorogenic complexes that extends across north america northeast into labrador of these a two mica monazite bearing granitic suite resides in central and southeastern arizona as part of a peraluminous subprovince that is bordered on the south southern arizona to sonora and west western arizona and adjacent portions of california and nevada by marginally metaluminous granites bearing biotite sphene hornblende and fluorite all of these 1 4 ga granites are distinctly more potassic iron enriched relative to mg and depleted in ca mg and sr in contrast to typical orogenic granitoids in general the large ion lithophile element enriched composition is a consequence of limited melting of a water deficient crustal source at depths greater than 25 37 km for the peraluminous granites this contrast is less extreme perhaps resulting from a larger degree of melting as a consequence of a greater metasedimentary component and water in its crustal source the anorogenic granitic magmas intruded into the upper crust at depths of 8 17 km or shallower at temperatures up to 790 c the most dramatic variation in the crystallization intensive parameters resides in the oxygen fugacity which spans three orders of magnitude relative to other anorogenic suites all of the magmas crystallized at elevated levels of o2 as reflected in their assignment to the anorogenic magnetite series yet a regionally significant rise in primary o2 levels unmatched elsewhere in the transcontinental belt occurs for plutons in western arizona including the holy moses and hualapai granites the most extreme case is the hualapai granite whose biotite fe fe mg ratios drop due to high o2 to a low of 0 27 down from more typical levels of 0 54 to 0 75 such extreme variations in primary levels of oxygen fugacity must be an indirect imprint of regional changes of the level of oxidation of the lower crust the high fo2 holy moses and hualapai plutons have intruded near the regional boundary between the metaluminous and peraluminous granites and appear to be imaging a major change in the level of oxidation of the lower crust this boundary is also approximately equivalent to significant changes in the nd and pb isotopic compositions of these granites and the metamorphic and magmatic character of the older orogenic terrane on a global scale the crust forming orogenies ended by 1 6 ga ago and the continents entered a long lived era dominated by localized extension and transcontinental intrusion of anorogenic potassic rapakivi granite mafic dike swarms charnockite and anorthosite the absence of orogenic deformation implies that plate consumption became intraoceanic during this time the profuse and widespread nature of the igneous activity has no phanerozoic analogue and is considered to be unique to the proterozoic a crustal overturn model ties the magmatism to heating within a largely undepleted subcontinental mantle the eventual rise of mantle plumes and the transfer of heat into the youthful undifferentiated proterozoic crust subsequent melting and rise of potassic granitic magmas from the lower crust leads to considerable crustal reorganization a process that would continue until both the mantle and crust reached a stable configuration

genesis of the giant zijinshan epithermal cu au and luoboling porphyry cu mo deposits in the zijinshan ore district fujian province se china a multi isotope and trace element investigation abstract the zijinshan ore district occurs as one of the largest porphyry epithermal cu au mo ore systems in south china including the giant zijinshan epithermal cu au deposit and the large luoboling porphyry cu mo deposit the mineralization is intimately related to late mesozoic large scale tectono magmatic and hydrothermal events the cu au mo mineralization occurs around intermediate felsic volcanic rocks and hypabyssal porphyry intrusions in this study we summarize previously available re os isotopes zircon u pb age and trace elements and sr nd pb isotope data and present new pb s and re os isotope data and zircon trace elements data for ore related granitoids from the zijinshan high sulfidation epithermal cu au deposit and the luoboling porphyry cu mo deposit in an attempt to explore the relationship between the two ore systems for a better understanding of their geneses the ore bearing porphyritic dacite from the zijinshan deposit shows a zircon u pb age of 108 106 ma and has higher zircon ce4 ce3 ratios 92 1568 average 609 but lower ti in zircon temperatures 588 753 c average 666 c when compared with the barren intrusions in the zijinshan ore district relative to the zijinshan porphyritic dacite the ore bearing granodiorite porphyry from the luoboling deposit show a slightly younger zircon u pb age of 103 ma but has similar or even higher zircon ce4 ce3 ratios 213 2621 average 786 and similar ti in zircon temperatures 595 752 c average 675 c these data suggest that the ore bearing magmatic rocks crystallized from relatively oxidized and hydrous magmas combined with the high rhenium contents 78 6 451 ppm of molybdenites the pb and s isotopic compositions of magmatic feldspars and sulfides suggest that the porphyry and ore forming materials in the luoboling cu mo deposit mainly originated from an enriched mantle source in contrast the ore bearing porphyritic dacite in the zijinshan cu au deposit might be derived from crustal materials mixing with the cathaysia enriched mantle the fact that the zijinshan cu au deposit and the luoboling cu mo deposit show different origin of ore forming materials and slightly different metallogenic timing indicates that these two deposits may have been formed from two separate magmatic hydrothermal systems crustal materials might provide the dominant cu and au in the zijinshan epithermal deposit cu and au show vertical zoning and different fertility because the gold transports at low oxygen fugacity and precipitates during the decreasing of temperature pressure and changing of ph conditions it is suggested that there is a large cu mo potential for the deeper part of the zijinshan epithermal cu au deposit where further deep drilling and exploration are encouraged

large scale porphyry type mineralization in the central asian metallogenic domain a review abstract a series of porphyry type cu mo au deposits including some giant world class deposits such as kounrad aktogai kal makyr oyu tolgoi and chalukou occur in the central asian metallogenic domain camd the outline of the camd almost overlaps with that of the central asian orogenic belt caob which is located between the east europe siberia tarim and north china cratons the camd comprises sparsely exposed tectonic slices of precambrian high grade metamorphic basement rocks that are sandwiched between phanerozoic accretionary complexes and arc rocks according to geological metallogenic geochronological and tectonic setting characteristics the camd comprises three metallogenic provinces 1 the kazakhstan cu au mo 2 the mongolia cu au and 3 the northeast china mo cu metallogenic provinces early paleozoic 490 to 440 ma and late paleozoic 330 to 295 ma large scale porphyry type mineralization in the kazakhstan metallogenic province is intimately associated with the evolution of the central tianshan yili northern tianshan kokchetav chingiz paleozoic arc system which was terminated by the late permian closure of the western segment of the paleo asian ocean in contrast the 370 ma and 240 ma porphyry type mineralization of the mongolia metallogenic province is related to the tuva mongolia arc collage system that was formed during the evolution of the paleo asian ocean in the paleozoic and the mongol okhotsk ocean in the early mesozoic furthermore the northeast china metallogenic province was affected by three distinct geodynamic processes that were associated with the paleo asian mongol okhotsk and paleo pacific oceans during the paleozoic 250 ma the early mesozoic 200 ma and the late mesozoic 200 90 ma respectively except for the early paleozoic cu mineralization at duobaoshan 480 ma and bainaimiao 440 ma the porphyry type mineralization of this metallogenic province is predominantly characterized by widespread mesozoic mo mineralization in general porphyry type deposits of the camd have geological structural metallogenic alteration and fluid characteristics which are consistent either with those related to the oceanic subductional arc settings of the circum pacific metallogenic domain or with those of the continental collisional environment in the tethyan metallogenic domain the involvement of highly oxidized intermediate to felsic magmas is fundamental for the formation of porphyry deposits even though the prevalent mash and slab melting models can be employed to interpret the genesis of some porphyry cu deposits in the camd a here newly suggested model which is based on pre enriched mafic lower crust and the subduction of a relictic mid oceanic ridge is thought to explain the large scale copper mineralization in the balkhash west junggar metallogenic belt of the kazakhstan metallogenic province nevertheless most of the porphyritic suites associated with the mo deposits in the northeast china metallogenic province have relatively depleted mantle like neodymium and hafnium isotopic compositions suggesting that the ore forming granitic magma may have predominantly been derived from juvenile lower crust upwelling of asthenosphere may have triggered the melting of the lower crust during post collisional extension subsequent to the closure of the paleo asian ocean in the triassic the subduction of the paleo pacific ocean in the jurassic and the thinning of the lithosphere caused by rollback of the paleo pacific plate in the cretaceous ancient crustal components were only locally found to have been involved in the magma source of several medium large mo deposits

geochronology and fluid inclusion studies of the lailisigaoer and lamasu porphyry skarn cu mo deposits in northwestern tianshan china abstract the lailisigaoer porphyry mo cu and lamasu porphyry skarn cu deposits are located in the northwestern tianshan orogenic belt which is in the northwestern china according to re os analysis of molybdenite the time of mineralization of the lailisigaoer deposit is 377 ma and shrimp zircon u pb analysis dates the ore hosted intrusion of the lamasu deposit to 378 ma five types of fluid inclusions fis have been identified in both deposits h 2 o rich inclusions co 2 bearing inclusions halite bearing inclusions methane rich inclusions and pure co 2 inclusions in the lailisigaoer deposit the early stage fluid of the quartz phenocryst belongs to a nacl h 2 o system with total homogenization temperatures t h ranging from 300 to 395 c with a mean salinity of 9 0 wt nacl in the ore forming stage the fluid develops into a h 2 o nacl co 2 system due to boiling and decarbonation the t h values and salinities cluster between 220 and 370 c and between 0 and 33 0 wt nacl respectively the hydrothermal characteristics of the late quartz calcite stage are similar to those of the meteoric fluid in the lamasu deposit the early stage fluid of the quartz phenocryst belongs to a nacl h 2 o system with t h values ranging from 245 to 459 c and a mean salinity of 6 0 wt nacl in the ore forming stage due to the contact metamorphism between the hydrothermal fluid and wall rock the fluid evolves to a nacl h 2 o ch 4 system the t h values and salinities cluster between 220 and 360 c and between 0 and 17 3 wt nacl respectively the fluid of the late quartz sulfide stage coincides with the meteoric fluid in the mineralizing fluid of the lailisigaoer deposit the captured temperatures and pressures are between 210 and 350 c and between 170 and 600 bars respectively which are consistent with fluctuation between hydrostatic and lithostatic pressure corresponding to the estimated paleodepths of 1 7 2 2 km boiling is the dominant mineralizing mechanism in the lailisigaoer deposit whereas the contact metamorphism between the magmatic hydrothermal fluid and country rocks is the dominant mechanism in the lamasu deposit both deposits are formed in the continental arc setting related to the southward subduction of the north tianshan oceanic slab beneath the yili central tianshan block

geology and origin of the post collisional narigongma porphyry cu mo deposit southern qinghai tibet narigongma is a poorly studied mo rich similar to 0 06 wt post collisional porphyry cu deposit located in southern qinghai province tibet 400 km northwest of the yulong porphyry cu mo au belt the narigongma deposit has a similar age 43 40 ma to porphyry deposits in the yulong belt but different ore assemblages the narigongma deposit is associated with eocene granodiorite and granite intrusions that were emplaced into a permian volcanic sedimentary rock sequence an similar to 43 3 ma biotite granite stock p1 porphyry is the earliest eocene intrusion and this was itself intruded by a number of smaller similar to 43 6 ma fine grained granite porphyry stocks p2 porphyry and several post ore quartz diorite porphyry dikes similar to 41 7 ma the main cu mo mineralization at narigongma is associated with the p1 porphyry hydrothermal alteration surrounding the deposits is generally characterized by concentric zones that range from an inner potassic zone outward to phyllic and argillic alteration zones and an outer propylitic zone hypogene mineralization at narigongrna was characterized by early stage precipitation of molybdenite during potassic alteration and late stage deposition of chalcopyrite during phyllic alteration deposition of both the mo and cu mineralization stages was caused by decreasing temperature a high degree of crystallization of the p1 porphyry occurred prior to fluid saturation that produced mo enrichment in the residual melt due to the incompatible behavior of mo however compatible cu was sequestered by the crystallizing phases and resulted in the generation of a high mo cu magmatic hydrothermal fluid and the final mo cu mineralization assemblage zircon epsilon hf t values of 4 1 to 7 9 are indicative of magma derivation from a depleted source these isotopic data coupled with other geochemical characteristics of the narigongma porphyry such as high sio2 and k2o contents low mgo contents and compatible element abundances and highly fractionated rare earth element patterns indicate a mixing model for the origin of the porphyry bodies generation of the post collisional ore forming porphyries occurred in two stages 1 partial melting of metasomatized phlogopite bearing lithospheric mantle that generated potassic to ultra potassic mafic melts and 2 underplating of such melts beneath thickened juvenile lower crust which triggered partial melting of the lower crust to produce the ore forming high k adakitic magma c 2013 international association for gondwana research published by elsevier b v all rights reserved

the internal geometry of nappes criteria for models of emplacement summary the geometric and stratigraphic properties of thrust sheets and fold nappes are controlled by the mechanisms by which they were initiated and emplaced thrust sheets that have developed by gravity gliding have their internal stratigraphies truncated by the basal thrusts which cut up section at the trailing edges in contrast thrust sheets that have developed by gravitational spreading have their internal stratigraphies truncated by the overlying thrust sheets and their basal thrusts cut up section at the leading edges fold nappes have complicated geometries and correlation of stratigraphy between successive nappes is difficult the basic geometric and stratigraphic properties of thrust sheets and fold nappes developed by different mechanisms may be used as criteria for testing the applicability of these mechanisms to particular areas of orogenic belts the valley and ridge province of the appalachians has geometric and stratigraphic properties consistent with thrust sheet development by gravitational spreading the western nappes of the central scandinavian caledonides are more complex but have properties suggesting development by buoyant upwelling of the orogen infrastructure there is however a lack of detailed cross sections of orogenic belts based on geophysical and or borehole data in addition to the geological data the interpretation of geological data in isolation is often too dependent on subjective information coloured by the mechanism preferred by the individual concerned

isotopic evidence for closed system anatexis at midcrustal levels an example from the acadian appalachians of new england we have investigated the sr and o isotope systematics of granitoid and metasedimentary samples from the central maine terrane cmt of new england granitoid samples were taken from interior and contact zones within the acadian aged 410 m y synmetamorphic and syntectonic kinsman quartz monzonite kqm which is a member of the new hampshire plutonic series metasedimentary samples were taken from silurian and devonian formations hosting the kqm initial sr isotope ratios sri and 18o values for the kqm range from 0 70799 to 0 71246 and 1 6 to 12 9 respectively and sri and 18o values of the metasedimentary rocks range from 0 70770 to 0 75008 and 6 2 to 14 1 respectively we observe a linear and slightly positive correlation between sri and 18o for interior kqm samples that can be duplicated by a mixing curve calculated for metasedimentary endmembers whereas the sri and 18o values of contact kqm samples cluster near the sri and 18o values of the metasedimentary rocks with which they are in contact mixing calculations provide no evidence for a measurable primitive mantle component in either interior or contact kqm samples and we conclude that the sr o isotopic composition of the kqm is most likely a reflection of isotopic heterogeneities inherited from a complex package of midcrustal metasedimentary source rocks we propose that the kqm is the product of midcrustal partial melting that was initiated due to excess thermal energy from the decay of anomalously high concentrations of heat producing elements in silurian source rocks within the cmt because we see no isotopic evidence for a lower crustal or mantle component in the kqm we suggest that midcrustal anatexis may have occurred as a closed system process requiring no accompanying mantle derived magma or above normal mantle heat flow

correspondence of ores of silver and gold with basement terranes in the american southwest the ratios of silver to gold produced from epigenetic ore districts of the american southwest reveal a consistency of value ranges differing by an order of magnitude that may be identified with either one or the other of two geologic terranes in which the ores occur a discriminating value of the ratio is about 17 5 1 the ratio of crustal abundance given by ahrens 1965 no further significance is attributed to this value at this time beyond the fact that it appears to establish a reasonable separation of values on the basis of geographic occurrence ores relatively enriched in ag occur in terranes floored by thick proterozoic clastic and paleozoic marine successions and ores relatively enriched in au lie above or within a proterozoic basement dominated by maficfelsic volcanic arc successions proterozoic granites occur in each region the values of the ratio are broadly consistent within each terrane irrespective of the age of ore formation the ore deposit style associated igneous rocks structural control differing interpreted styles of subduction and weathering histories these characteristics and associations support a hypothesis that metallogenic signatures of ore districts in this region are fundamentally related to the crust in which the ores occur

chemical and isotopic compositions of absaroka granitoids southwestern montana contents of major and most trace elements of granitoids in three intrusions associated with the cretaceous independence volcanic complex montana correlate well with sio2 major element contents in granitoids in each intrusion are accurately modeled as mixtures of minimum melts and phenocryst assemblages presumably restite restite assemblages are hypersthene augite plagioclase hornblende plagioclase and biotite plagioclase quartz residues of melting are granulite or amphibolite melts in two of the bodies were lree enriched but unfractionated in mree and hree ree patterns are consistent with residues dominated by pyroxene or amphibole and feldspar initial 207pb 204pb and 206pb 204pb of granitoids define a line interpreted as a secondary isochron established during crustal homogenization 3 3 ga ago the relatively low of source rocks 8 25 suggests that they did not spend long in u rich environments source regions had variable trace element patterns th pb and u pb were correlated rb sr and sm nd moderately well correlated but rb sr and u pb were decoupled this is consistent with poor correlation of rb sr and ba with sio2 in some granitoids and may suggest that minor phases that concentrate these elements were inhomogeneously distributed in source regions the source probably consisted of lree rich rb poor metamorphic rocks archean amphibolites exposed in the beartooth mountains are similar to the postulated source materials they contain plagioclase hornblende minor quartz biotite and muscovite and have low rb sr and high lree hree certain trace element characteristics of the granitoids indicate that the deep crust in this part of montana may be dominated by metamorphosed mafic intermediate lavas that formed on the sea floor metapelites intercalated with amphibolites at the surface were rare in granitoid source regions this buried supracrustal pile was isotopically homogenized 3 3 ga ago although some material melted 2 7 ga ago to form granites that dominate the exposed basement enough remained fertile that heating by mantle derived magmas 85 90 ma ago produced the granitic rocks at independence

crust mantle interaction in continental arcs inferences from the mesozoic arc in the southwestern united states arc magmas ranging in composition from basaltic andesites to rhyolites and intrusive equivalents were emplaced into the western margin of the north american craton starting in late triassic time giving way to rift0related sedimentation in the late jurassic the region of this study cuts across proterozoic basements of contrasting nd model ages 1 7 1 8 ga average nd 11 in eastern arizona and 2 0 to 2 3 ga average nd 18 in western arizona and eastern california bennett and depaolo 1987 the mesozoic rocks have initial nd of 3 4 to 6 4 in the eastern part of the study area and 7 1 to 9 2 in the western part all of the rocks have elevated 87sr 87sr initial ratios 0 706 trends in initial nd values of mesozoic arc rocks are directly correlated with the nd model ages of the basement through which they passed simple two component mixing calculations indicate that recycled continental crust in the arc magmas represents on average about 65 a minimum of 35 mantle input into continental arc magmas as recent as the mesozoic represents a significant contribution to the growth of the continental crust in the absence of a return flow of continental material into the mantle of similar magnitude in a detailed study in the santa rita mountains arizona there is a pattern of increase of nd with time early basaltic andesites have more negative nd than later felsic rocks a correlated pattern of depletion with time is also observed with trace element and major element data we attribute this either to progressive hybridization of the lower crust by repeated injection of mantle magmas or the progressive thinning of the continental crust during prolonged arc magmatism the present data do not allow distinction between the two models progressive decrease in crustal contribution to arc magmas with time may be an important feature of continental arc evolution hybridization of the lower crust due to repeated injection of mantle melts during arc magmatism may help contribute to small scale heterogeneities in lower crust inferred from seismic and xenolith data similarly whether there is a well defined moho or sharp crust mantle boundary in any given segment of the continental crust may in part depend on the extent of crust modification as a result of continental arc magmatism

late brittle deformation in a caledonian ductile thrust wedge new evidence for gravitational collapse in the moine thrust sheet sutherland scotland abstract in the ductile regions of orogenic wedges late brittle structures formed at shallow crustal depths have received little attention however they are important as they of ten record the final stages in deformational history during uplift and erosion of the orogen in the moine rocks of sutherland late caledonian brittle folds and low angle faults post date ductile structures formed during wnw nw directed thrust movements earlier in the same orogenic event in the western moine nappe the late structures display geometries which indicate that they formed during regionally ese directed extensional movements down the dip of the pre existing regional foliation these late structures are correlated with similar wnw directed extensional low angle faults recognised in the moine thrust zone south of the assynt culmination both are thought to have formed in response to late caledonian gravity induced thinning of the moine thrust wedge and both pre date devonian extension associated with the formation of the west orkney basin along strike changes in the location and sense of extensional movements north and south of the assynt culmination are explained by changes in the pre existing structural geometry of the caledonian ductile thrust nappes within the moine hence earlier deformation patterns are thought to exert important controls over later events in an evolving orogenic wedge

petrogenesis of the highly potassic 1 42 ga barrel spring pluton southeastern california with implications for mid proterozoic magma genesis in the southwestern usa syenites from the barrel spring pluton were emplaced in the early proterozoic mojave crustal provine of southeastern california at 1 42 ga all rocks even the most mafic are highly enriched in incompatible elements e g k2o 4 12 wt rb 170 370 ppm th 12 120 ppm la 350 1500xchondrite la ybn 35 100 elemental compositions require an incompatible element rich but mafic or ultramafic source trace element models establish two plausible sources for barrel spring magmas 1 lree enriched garnet websterite with accessory apatite rutile enriched lithospheric mantle and 2 garnet amphibolite or garnet hornblende granulite with enriched alkali basalt composition also with accessory apatite rutile mafic lower crust nd and pb isotopic ratios do not distinguish a crust vs mantle source but eliminate local mojave province crust as the principal one and indicate that generation of the enriched source occurred several hundred million years before emplacement of the barrel spring pluton 1 40 1 44 ga potassic granites are common in southeastern california suggesting a genetic link between the barrel spring pluton and the granites however although the same thermal regime was probably responsible for producing both the granitic and syentic magmas elemental and isotopic compositions preclude a close relationship isotopic similarity of the barrel spring pluton to 1 40 1 44 ga granites emplaced in the central arizona crustal province to the east may imply that a common component was present in the lithosphere of these generally distinct regions

formation of the giant chalukou porphyry mo deposit in northern great xing an range ne china partial melting of the juvenile lower crust in intra plate extensional environment abstract the chalukou porphyry mo deposit 2 46 mt 0 087 mo located in the northern great xing an range ne china is the largest mo deposit discovered in china so far the host rocks consist of aplite porphyry granite porphyry and quartz porphyry and are intruded into lower ordovician intermediate felsic volcanic sedimentary rocks and pre ore monzogranite and are cut by post ore feldspar porphyry diorite porphyry and quartz monzonite porphyry here we present the zircon u pb ages whole rock geochemistry sr nd isotopic and zircon hf isotopic data for the pre ore syn ore and post ore intrusive rocks the chalukou ore forming porphyries intruded during 147 148 ma and have high silica alkali rich metaluminous to slightly peraluminous compositions and are oxidized they are enriched in large ion lithophile elements e g k rb u and th light ree and depleted in high field strength elements e g nb p and ti depletions in eu ba sr nb ta p and ti suggest that they have experienced strong fractional crystallization of plagioclase biotite hornblende and accessory minerals the pre ore monzogranite 172 ma also belongs to the high k calc alkaline series highly fractionated ree patterns la yb n 19 6 21 7 high values of sr y 54 69 and la yb 29 32 are adakite like geochemical features the post ore rocks 141 128 ma have similar geochemical characteristics with ore forming porphyries except that quartz monzonite porphyry shows no ba sr negative anomaly all intrusive rocks have relative low initial 87sr 86sr 0 705413 0 707889 and end t values 1 28 to 0 92 positive ehf t values 2 4 to 10 1 and young two stage nd and hf model ages tdm2 nd 863 977 ma tdm2 hf 552 976 ma these geochemical and isotopic data are interpreted to demonstrate that the ore forming porphyries formed by partial melting of the juvenile lower crust caused by underplating of mafic magmas in an intra plate extensional setting the pre ore monzogranite formed by partial melting of thickened lower crust in a collisional setting caused by closure of mongol okhotsk ocean the post ore feldspar porphyry shares a similar magma source with ore forming porphyry but the quartz monzonite porphyry has a relatively deeper magma source region and has not experienced as much fractional crystallization the transformation from middle jurassic compression to late jurassic extension created favorable conditions for the generation and emplacement of the ore forming magma the juvenile lower crust provided the main source of molybdenum for chalukou deposit enrichment of mo by fractional crystallization played an important role in concentrating mo during formation of the chalukou mo deposit the age 147 ma high fluorine and associated pb zn deposits are all different from other major porphyry mo deposits in ne china chalukou is a new mineral deposit type in the great xing an range

progressive mixing of isotopic reservoirs during magma genesis at the sierrita porphyry copper deposit arizona inverse solutions abstract trace element and sr and nd isotopic compositions have been determined for a suite of calc alkaline rocks from southeastern arizona the suite consists of andesitic and rhyolitic rocks 67 m y old intruded by granodiorite and granite 58 62 m y old it is situated within proterozoic basement of 1 7 to 1 65 ga age isotopic composition and chemical evolution are well correlated throughout the suite the andesite has the least negative nd tigneous 4 3 and smallest 87 sr 86 sr 0 0 7069 it is also the oldest and chemically most primitive having the lowest concentrations of rb sio2 and highest concentrations of the transition elements these parameters change through the system to the youngest unit granite which has the most negative nd 8 5 the greatest 87 sr 86 sr 0 0 7092 and is most chemically evolved we interpret these trends as resulting from a continuous process of progressive assimilation in which mafic magmas invade and incorporate continental crust the assimilated continental crust was probably intermediate to mafic in composition and of amphibolite grade phase relations among minerals indicate that it was hydrous and oxidizing also if the granite is in isotopic equilibrium with the basement its nd of 8 5 implies a 147 sm 144 nd of 0 13 to 0 14 for the assimilant characteristic of intermediate to mafic rather than felsic rocks inverse methods have been applied to equations for assimilation and fractional crystallization whose use assumes periodic tapping of a single magma body such modelling yields insight into the size and chemistry of the magma system

source regions of granites and their links to tectonic environment examples from the western united states this review in honor of ilmari haapala s retirement reflects on lessons learned from studies of three granitic systems in western north america 1 mesoproterozoic samples from west texas and east new mexico 2 laramide granitic systems associated with porphyry copper deposits in arizona and 3 granites of the colorado mineral belt the studies elucidate relationships amongst tectonic setting source material and magma chemistry mesoproterozoic basement samples are from two different felsic suites with distinct elemental and isotopic compositions the first suite the plutonic province is dominantly magnesian calc alkalic to alkali calcic and metaluminous it has low k2o na2o and rb sr and nd model ages of 1 56 to 1 40 ga the second suite the panhandle igneous complex is magnesian metaluminous alkalic and is part of the mesoproterozoic belt of magmatism that extends from finland to southwestern united states samples from the panhandle igneous complex demonstrate three episodes of magmatism the first pulse was intrusion of quartz monzonite at 1380 to 1370 ma the second was comagmatic epizonal granite and rhyolite at 1360 to 1350 ma both of these rock types are high k to slightly ultra high k the third pulse at 1338 to 1330 ma was intrusion of ultra high k quartz syenite nd model ages 1 94 to 1 52 ga are distinct from those of the plutonic province and systematically older than crystallization ages implying a substantial crustal input to the magmas at the sierrita porphyry copper deposit in the mazatzal province of southeastern arizona trace element sr and nd isotopic compositions were determined for a suite of andesitic and rhyolitic rocks 67 ma intruded by granodiorite and granite isotopic composition and chemical evolution are well correlated throughout the suite andesite has the least negative initial end 4 3 and lowest 87sr 86sri 0 7069 it is also the oldest and chemically most primitive having low concentrations of rb sio2 and high concentrations of transition elements these parameters change through the system to the youngest unit granite which has the most negative end 8 5 the highest 87sr 86sri 0 7092 and is chemically most evolved correlation between chemical and nd isotopic evolution probably resulted from a continuous process of progressive assimilation in which mafic magmas invade and incorporate continental crust deposits in arizona with end values more negative than the 8 5 of sierrita lie in the older yavapai province in the northwestern part of the state the difference in the most negative epsilon nd implies that nd isotopic signature is sensitive to the age of the precambrian domain the granites from the colorado mineral belt were emplaced during the transition from laramide convergence to mid tertiary extension three different groups of granites are recognized the first is laramide and was formed during assimilation fractional crystallization involving lower crustal mafic source materials the second and third groups are mid tertiary and represent intracrustal melting of heterogeneous sources this change in source regions and melt regimes in transition from convergence to extension is fundamental to the mesozoic and cenozoic evolution of western north america

late cretaceous to early eocene magmatic evolution of the laramide arc in the nacozari quadrangle northeastern sonora mexico and its regional implications abstract late cretaceous to early eocene volcanic and plutonic rocks that crop out in the nacozari quadrangle compose the laramide magmatic arc in northeastern sonora northwestern mexico the purpose of this work is to characterize the arc rocks based on new cartography stratigraphy u pb and k ar geochronology and major trace and isotope geochemical data and interpret them in the regional context of evolution of the arc the study area lies within the proterozoic mazatzal crustal block which is limited to the south by the caborca block the volcanic rocks regionally correlate with the tarahumara formation and consist of volcanic flows breccias tuffs and volcaniclastic sandstones with an estimated thickness of 4 km they range in composition from andesite to rhyolite and have isotopic ages from 76 8 0 4 to 57 1 0 4 ma the granitic plutons and rhyolitic domes that intrude them yielded ages from 59 3 0 8 to 53 3 1 6 ma initial 87 sr 86 sr and epsilon nd values for these rocks vary from 0 70553 to 0 70841 and 3 7 to 8 5 respectively and have 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb isotope ratios that range from 18 05 to 19 05 15 52 to 15 63 and 38 25 to 39 07 respectively regional integration of our u pb ages suggests that the volcanic activity lasted between ca 81 and 57 ma with two main peaks of activity at 74 5 and 61 ma similarly regional magmatic activity indicated by dated plutons initiated at ca 91 and ended by 50 ma after main peaks of activity at 71 and 60 55 ma the plutonism between 91 and 80 ma was subordinate and regionally restricted to coastal and central sonora and might represent an older event unrelated to the laramide arc two k ar cooling ages of 55 4 0 7 and 48 5 0 7 ma obtained from la purica granite dated at ca 59 ma u pb in the study area correlate regionally with a possible event of rapid uplift between 68 and 50 ma the geochemical composition of the studied rocks indicate high k calc alkaline metaluminous to weakly peraluminous compositions typical of subduction arc related magmas which characterize the laramide magmatic belt in northwestern mexico the nd sr and pb isotope compositions of these and other samples documented for northeastern sonora closely correlate with isotope signatures of the mazatzal crustal block in southeastern arizona and differ from those in the caborca block which display affinity with the mojave yavapai province the data also allow to best constrain the location of the boundary between the mazatzal and caborca crustal blocks in east central sonora

latest cretaceous and early tertiary orogenesis in south central arizona thrust faulting regional metamorphism and granitic plutonism rocks in a number of mountain ranges in southernmost central arizona are juxtaposed by thrust faults regionally metamorphosed and intruded by garnet two mica granites field relations and k ar and u pb isotopic geochronology indicate that thrust faulting metamorphism and granitic plutonism were closely related aspects of a latest cretaceous and early tertiary orogenic episode the regionally metamorphosed rocks chiefly greenschist facies quartzofeldspathic schists were derived from jurassic and cretaceous sedimentary volcanic and plutonic rocks in five ranges these metamorphic rocks are overlain along synmetamorphic thrust faults by precambrian gneiss or late jurassic or late cretaceous plutonic rocks in three additional ranges upward increase of textural grade within the metamorphic rocks and analogy with the areas of exposed thrust faults indicate the likelihood of a concealed thrust fault flanking the range seven of these eight thrust faults have single lower plates but one thrust is underlain by a duplex consisting of several imbricate structural sheets separated by mylonitic tectonic slides areal structural relations and the regional arrangement of distinctive jurassic igneous rock units strongly suggest that one large range the baboquivari mountains and several smaller ranges are fensters in a thrust fault system of regional extent and that several adjacent ranges are allochthonous the regionally metamorphosed rocks are intruded by synmetamorphic to postmetamorphic early tertiary leucocratic granites characterized by various combinations of accessory biotite muscovite and garnet at least two of these granites contain inherited precambrian zircon indicative of generation by crustal anatexis k ar and or u pb isotopic ages of premetamorphic granites metamorphic rocks thrust zone mylonites synmetamorphic granites and metamorphogenic fissure veins indicate that the orogenic episode commenced in late cretaceous time and culminated in early tertiary time 58 to 60 m y ago the observed and inferred close spatial and temporal relations between thrust faulting regional metamorphism and granitic plutonism lead to the following hypothesis for orogenesis in south central arizona crustal compression caused overthrusting of crystalline rocks resulting in crustal thickening and crustal thickening and conductive and magmatic heat flux from the mantle together set up a thermal regime within which regional metamorphism and the generation and emplacement of the anatectic granites took place

formation and tectonic evolution of southeastern china and taiwan isotopic and geochemical constraints abstract the southern part of china consists of the proterozoic yangtze craton and the phanerozoic south china foldbelts including the himalayan foldbelt of taiwan models for continental growth have been many and controversial isotopic and geochemical data from mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of southeastern china and to evaluate whether the young phanerozoic foldbelts are representative of old rejuvenated landmass whether they characterize crustal accretion through successive subduction processes hence suggesting a net growth of continental mass or whether they represent some intermediate situation available sm nd isotopic data for phanerozoic granitoids and metasediments from the south china foldbelts and taiwan invariably show proterozoic model ages t dm ranging from 1 to 2 5 ga with a mean of 1 54 0 30 1 ga all rocks have negative nd t values 2 to 15 suggesting variable but important contributions of old continental materials to the sources of the phanerozoic rocks obviously they do not represent wholesale growth of continental mass the granitoids of the south china foldbelts have multiple origins as viewed from their chemical and isotopic characteristics secular geochemical variation has been established for inland granitoids of proterozoic to mesozoic age their high i sr values 0 710 0 737 suggest that most granitoids are essentially anatectic products of ancient continental crust this is compatible with remelting via microcontinental collision or terrane accretion repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization mesozoic granitoids excluding a type alkaline granites in the coastal region and taiwan show relatively low i sr 0 705 0 710 and high nd values implying that greater amounts of mantle components have been added to ancient continental material in the generation of these rocks this means that mesozoic magmatism in the coastal region resulted from subduction of a paleo pacific plate kula beneath the asian continent the overall geochemical evidence seems to be consistent with a model of serial collisions between microcontinental blocks for the bulk of the south china foldbelts the latest arc continent collision began about 4 ma ago in eastern taiwan

geochemical and nd isotopic systematics of granites from the arunta inlier central australia implications for proterozoic crustal evolution geochemical and sm nd isotopic results are reported for granites from the proterozoic arunta inlier of central australia these combined with new geochronological data for the granites zhao and bennett 1995 allow important constraints to be placed on proterozoic tectonic and crustal evolution in central australia granites from the arunta inlier can be divided into three major geochemical groups a calcalkaline trondhjemitic group cat a high heat production group hhp and a volumetrically significant main group the cat group which occurs only in the southern margin of the inlier is characterised by high na2o nak sr krb and sry and relatively low k2o rb rbsr th u ree nb and y analogous to calc alkaline suites occurring in modern convergent plate margins the hhp group which occurs mainly in the interior of the arunta inlier and is spatially associated with the main group is characterised by high k rb th u rbsr and rbzr and relatively low sr ba nak krb barb mgo cr and ni the main group which occurs throughout the arunta inlier is geochemically intermediate between the cat and hhp groups it is geochemically analogous to the 1880 1850 ma old barramundi igneous association recognised in other proterozoic terrains of central australia and can be further subdivided into four age subgroups 1820 1780 1750 1650 and 1615 1600 ma respectively all three groups show similar negative nb anomalies on the trace element normalized diagrams despite the geochemical diversity of the arunta granites no correlations between the nd isotopic and geochemical signatures are observed the ranges of initial nd values and nd depleted mantle model ages tnddm for the three groups of granites overlap with each other overall there are two groups of tnddm ages the most common ranging from 2 33 to 1 96 ga and the other from 1 83 to 1 72 ga although initial nd values of the granites show large variations there is a general trend for the nd values to increase i e become less negative with decreasing crystallization ages the large geochemical and isotopic variations of the arunta granites reflect considerable heterogeneity in the sources of the granites and do not support a uniform 2 3 2 1 ga old barramundi type underplate source for the origin of the granites the combined geochemical and nd isotopic data suggest the sources of the granites contain at least two main components an palaeoproterozoic mantle derived component and an older crustal component the older crustal component was incorporated into the source region of the granites either through magma assimilation of crustal materials at lower crustal levels or more probably via sediment subduction and mantle wedge metasomatism the increasing nd values with decreasing crystallization ages may be a result of progressively increasing proportions of newly accreted island arc materials being incorporated in the subducted sediments alternatively a juvenile mantle derived component may have been added to the source region of the younger granites it is apparent that the nd isotopic signatures in the granites has resulted from complex processes and neither simple mixing nor simple two stage protolith models can as yet satisfactorily explain the observations the petrogenesis of the three geochemical groups of granites can be interpreted in a plate tectonics scenario it is considered that the cat group was formed by fractionation of arc type magmas and or partial melting of arc related intrusions or underplates in a subduction related continental margin setting whilst the formation of the main group may involve partial melting of fractionated and or modified arc related underplates but not necessarily in a subduction environment the younger hhp group was probably generated by remelting of the coexisting main group during subsequent tectonothermal events

asynchronous formation of the adjacent epithermal au cu and porphyry cu mo deposits in the zijinshan orefield southeast china abstract adjacent high sulfidation epithermal hse and porphyry deposits often have similar cu au metal association suggesting they are cogenetic and formed contemporaneously the zijinshan orefield zof is the largest au producer in china and contains a series of hse au cu and porphyry cu mo deposits this study presents new 1 muscovite 40ar 39ar ages for the hse deposit in this area new 2 zircon laser ablation inductively coupled plasma mass spectrometry la icp ms u pb ages for felsic igneous rocks associated with the epithermal and porphyry mineralization and 3 new zircon lu hf isotopic data for these intrusions all of which provides insights into why these adjacent epithermal au cu and porphyry cu mo deposits have different metal associations the age data indicate that the alunite dickite alteration related to the hse au cu mineralization formed before ca 110 ma and the main hse au cu mineralizing event occurred at ca 113 ma in comparison the adjacent porphyry cu mo mineralization formed at ca 104 ma ca 9 myr after the hse event the volcanic rocks associated with the hse au cu mineralization yield zircon ehf t values from 4 1 to 0 3 whereas the cu mo mineralized porphyry has lower zircon ehf t values 4 5 to 1 2 suggesting that the magmas that formed the latter intrusion were derived from a source containing more crustal material than the magmas associated with the hse mineralization the differences in the timing of mineralization and the sources of the magmas indicate that the adjacent hse and porphyry deposits in the zof formed from different magmatic hydrothermal systems that controlled the different metal associations of the mineralizing systems this means that future mineral exploration within the zof should target porphyry au cu deposit at depths that is genetically related to the hse au cu deposit the results also show that not all adjacent porphyry and epithermal deposits especially those with different metal associations are cogenetic

highly differentiated juvenile crust derived magmas linked with the xilekuduke porphyry mo cu deposit in east junggar nw china abstract the east junggar region links the kazakhstan junggar plate with the siberian craton along the western part of the central asian orogenic belt among the major ore deposits in this region the xilekuduke molybdenite deposit is a unique example of mo dominated porphyry molybdenum and copper mineralization here occur as disseminated sulfides or veinlets mainly in granite porphyry and monzogranite with a prominent alteration from an inner potassic through sericitic to an outer propylitic zone zircon la icp ms u pb ages indicate that the granite porphyry and monzogranite were emplaced at 326 4 2 ma and 328 2 1 8 ma respectively both rocks show enrichment in light rare earth elements lree and rb k sr hf zr but depletion in nb ta ti and p suggesting magma generation in a post collisional setting a relatively high oxidation state is inferred from zircon ce values and oxygen fugacity of parental magma the ore hosted intrusions also show high differentiation index di indicating a highly oxidized parental magma and prolonged differentiation process the range of zircon ehf t values 11 5 to 17 young zircon hf model ages and consistent but slightly low zircon 18o values 4 84 to 5 20 together with the range of mg 35 53 suggest derivation of the parental magma through partial melting of juvenile crust with minor contribution from mantle components and sediments we propose that melting of juvenile oceanic components at depth with high degree of differentiation played a significant role in generating the mo mineralization in xilekuduke deposit within a post collisional setting in the east junggar domain

recumbent folds key structural elements in orogenic belts abstract this review has two main parts the first of them presents existing ideas and data related to recumbent folds reviewing aspects such as the physical conditions of the development of these folds the strain inside the folded layers the kinematic mechanisms of their formation the role of gravitational forces the tectonic context of their development and the structures associated with them in the second part the above ideas are discussed and possible mechanisms for the development of these folds are presented it is proposed that initial perturbations of the layers are essential to give rise to the asymmetry of recumbent folds these perturbations may be non planarities of the layering or may be linked to the existence of a core or basement of competent rock that hinders the normal propagation of the deformation this could explain why many large recumbent folds have a root zone deformation with an important component of simple shear is a general condition for the formation of recumbent folds in areas with very low grade metamorphism competent layers often play an active role during the deformation and undergo buckling with the development of an overturned fold limb which can be stretched and thinned to finally produce a pair of recumbent folds separated by a thrust in areas with low or medium metamorphism buckling under a simple shear regime is probably the most important mechanism for producing large folds with gentle or moderately dipping axial surfaces subsequent kinematic amplification by coaxial strain components with vertical maximum shortening is important for the formation of recumbent folds these components involve a sub horizontal stretching that can cause a problem of strain compatibility and give rise to a basal thrust in areas deformed under high p and t conditions recumbent folds can develop by flow perturbations and kinematic amplification of folds this is probably a common mechanism in ductile shear zones

migration of tertiary volcanism in the southwestern united states and subduction of the mendocino fracture zone abstract a compilation of 417 isotopic dates on mid and late cenozoic igneous rocks from the southwestern united states shows that volcanism migrated northward with time the principal locus of volcanism at any given time was an east west band that corresponded closely with the calculated position of the subducted mendocino fracture zone mfz under the north american plate this correspondence supports the theory that volcanism was triggered by subduction of the mfz which was a major 1 km north facing topographic step in the farallon plate both volcanism and the mfz moved northward at about 3 1 cm year andesites and rhyolites show close correspondence to mfz passage but many basalts were erupted significantly later cooling dates on basement rocks in southern arizona cluster at the time the mfz passed under that area earlier models proposing rapid late tertiary steepening of the subducted farallon plate were based on a westward sweep of volcanism our compilation shows no evidence for such a westward sweep

metallogenesis and ore controls of cenozoic porphyry mo deposits in the gangdese belt of southern tibet abstract the gangdese is a newly explored porphyry copper ore belt in china except for the cu mo au porphyry deposits there are some mo cu w porphyry and skarn deposits in this belt two pulses of molybdenite mineralization are recognized in the central lhasa subterrane with ancient continent crust including the paleocene eocene 65 52 ma porphyry mo and skarn mo w deposits formed during the rollback of neo tethyan oceanic slab in collisional setting and miocene 21 15 ma porphyry mo cu deposits generated in the postcollisional setting the gangdese copper deposits also occur during these two periods but are distributed in the southern lhasa subterrane dominated by juvenile crust through mantle derived magmatism resulting from neo tethyan ocean lithosphere subduction the intrusions related to molybdenite mineralization have relatively lower bulk rock e nd t and higher 87 sr 86 sr i values lower zircon e hf t values and older hf model ages lower molybdenite re contents and more radiogenic pb isotopes than the coeval copper related porphyries in the gangdese belt in addition the miocene mo cu related intrusions generally have lower zircon ce 4 ce 3 ratios than the miocene cu mo related intrusions these data indicate that more contributions from mature continental crustal materials play crucial role in the generation of mo than cu porphyry mineralization in the gangdese belt the eocene mo related intrusions are characterized by high sio 2 68 76 and k 2 o 5 1 5 9 concentrations enrichment of large ion lithophile elements lile depletion of high field strength elements hfse and low sr y 7 5 23 8 ratios their sr nd isotope compositions e nd t 3 4 to 4 6 87 sr 86 sr i 0 70622 0 70679 indicate that they are associated with partial melting of mantle wedge mixing with significant amounts 55 65 of middle upper crustal materials the miocene mo cu related intrusions have relatively high sio 2 64 73 and k 2 o 1 9 4 8 contents and are characterized by enrichment of lile depletion of hfse and high sr y ratios 55 189 their sr nd isotope compositions e nd t 4 6 to 3 4 87 sr 86 sr i 0 70622 0 70679 are indicative of derivation from remelting of previously subduction modified tibetan lithosphere with significant amounts 50 70 of middle upper crustal materials for the gangdese mo cu porphyry mineralization mo metal was suggested to be derived from the middle upper crustal materials particularly the carbonaceous permian marine sedimentary whereas cu metal to be sourced from the gangdese miocene cu fertile magmas the exploration targeting of the gangdese molybdenite deposits should be focused on southern part of the central lhasa subterrane where the carbonaceous permian strata occur the occurrence of mo cu porphyry deposits could provide clue for targeting cu mo porphyry deposits in the gangdese belt the gangdese molybdenite deposits share many similarities with the east qinling molybdenite deposits such as type of ore deposits geodynamic setting of their formation variable mo grades and high f contents

structural evolution of the southern baboquivari mountains south central arizona and north central sonora structural analysis of metamorphic tectonites low angle faults and planar dilational dike swarms in the southern baboquivari mountains reveals a complex mesozoic through middle tertiary history comprising multiple periods of deformation locally preserved rootless folds probably represent jurassic soft sediment deformation or tectonic deformation that pre dated the main episode of late cretaceous through early tertiary tectonism the latter involved thrust faulting isoclinal folding ductile strain and transposition of bedding into foliation greenschist to lower amphibolite facies regional metamorphism and late to post metamorphic intrusion of an early tertiary peraluminous granite pluton intrusion of the pluton was accompanied by minor folding of foliation in the country rock and subsequent brittle extension with emplacement of a granitic dike swarm middle tertiary metamorphic core complex deformation involved mylonitization accompanied and closely followed by detachment faulting and intrusion of microdiorite and lamprophyre dikes the southern baboquivari mountains thus record two independent tectonic episodes the first compressional and the second extensional both episodes are marked by a progression from ductile to brittle deformation orientations of late metamorphic extension fractures and the granitic dike swarm indicate ne sw crustal extension in late cretaceous through early tertiary time the middle tertiary extension direction nne ssw is indicated by the attitudes of post mylonite mafic dikes poles to these dikes are parallel to mylonitic lineation these extension directions documented in the southern baboquivari mountains are typical of the southern papago terrane of south central arizona in contrast the rest of southern arizona is characterized by nnw sse extension during late cretaceous through early tertiary time and ene wsw extension during middle tertiary time the anomalous extension directions of the southern papago terrane probably reflect deviations from regional strain patterns in a terrane with inherited anomalous crustal rheology and or thickness

common pb isotopic compositions of the lima arequipa and toquepala segments in the coastal batholith peru implications for magmagenesis abstract common pb isotopic compositions for 65 feldspar samples from the 188 37 ma old gabbroic to monzogranitic plutons of the peruvian coastal batholith show changes along strike that can be related to variable contamination of mantle derived magmas by the local precambrian basement results have the following isotopic ranges 206 pb 204 pb 17 580 20 803 207 pb 204 pb 15 555 15 709 and 208 pb 204 pb 38 104 41 177 with averages of 206 pb 204 pb 18 630 207 pb 204 pb 15 610 and 208 pb 204 pb 38 500 the gabbroic dioritic and tonalitic plutons north and east of lima the lima segment have ratios similar to the isotopically homogeneous reservoir identified by tilton 1979 tilton and barreiro 1980 and barreiro and stern 1982 for rocks in central and southern chile the homogeneous reservoir has been suggested to be enriched subcontinental mantle more siliceous rocks granodiorites and monzogranites in the lima segment have considerably higher ratios 206 pb 204 pb 18 680 20 803 207 pb 204 pb 15 610 15 709 and 208 pb 204 pb 38 500 41 177 nine of ten monzogranites from the ring dike complexes in the lima segment define a linear array with a slope of 0 1143 correlation coefficient 0 9398 and a pb isochron age of 1 9 ga this isochron age has no simple chronological meaning although it may represent a component of sedimentary debris derived from 1 9 ga crustal materials feldspars from plutons in the arequipa and toquepala segments south of lima tend to have low pb isotopic ratios 206 pb 204 pb 17 580 18 603 207 pb 204 pb 15 555 15 633 and 208 pb 204 pb 38 104 38 749 the ratios plot between the isotopic signatures of local precambrian granulites and gneisses and the chile type enriched subcontinental magmatic reservoir indicating that these end members were the principal magma sources the oldest plutonic rocks in the segments early to mid jurassic are closest to the pb isotopic ratios of the precambrian basement contamination of plutons in the arequipa and toquepala segments by unradiogenic pb from the precambrian basement and lack of it in the lima segment supports crustal models by couch et al 1981 and jones 1981 which show a thick precambrian basement layer throughout southern peru and an extremely thin layer beneath the lima segment

nd and sr isotopic compositions of lower crustal xenoliths from north queensland australia implications for nd model ages and crustal growth processes abstract sr and nd isotopic analyses of granulite facies lower crustal xenoliths from northern queensland australia fall on a mixing array on a 87 sr 86 sr vs 143 nd 144 nd diagram at 300 ma this was a time of intense orogeny in northern queensland attended by granitic magmatism in the upper crust and granulite facies metamorphism in the lower crust ion microprobe zircon dating indicates that most of the xenoliths formed at this time the sr and nd isotopic compositions of these rocks are therefore interpreted to have resulted from large scale mixing in the lower crust between mantle derived basaltic melts and isotopically evolved early proterozoic continental crust both end members are represented in the xenolith suite depleted mantle nd model age tdm ages for meta igneous granulite xenoliths having appropriate 147 sm 144 nd i e between 0 12 and 0 15 range from 1 9 to 2 2 ga for mafic melt like xenoliths and 1 2 to 1 4 ga for felsic melt like xenoliths however zircon ages on these same samples show that their protoliths crystallized during the permo triassic orogeny thus the old tdm ages for the mafic xenoliths do not accurately reflect their crustal residence ages possibly due to crustal assimilation or their derivation from an enriched mantle source this is a common feature of mafic granulite xenoliths the world over and highlights the difficulty in determining the age of mafic underplates hence the timing of crustal growth from tdm ages because the felsic melt like xenoliths lie on the mixing array their mid proteozoic tdm ages are likely to have resulted from mixing and therefore represent an average crustal residence age the combined data suggest that significant crustal growth and reworking occurs in the lower crust during phanerozoic crustal orogenies

isotopic evidence for the provenance of turquoise in the southwestern united states the archaeological record shows that turquoise was widely mined and highly valued by pre hispanic societies in the southwestern united states and it has long been assumed that much of the turquoise noted in ancient mesoamerica was traded from this region however little is understood about the acquisition and exchange of turquoise by native american societies because the geological sources of most turquoise artifacts from archaeological sites in the southwestern u s and mexico are not known we evaluate the potential for pb and sr isotopic ratios to indicate the geological provenance of turquoise artifacts recovered from these regions pb and sr isotopic measurements were made on 137 geological samples of turquoise from 19 mining districts across the southwestern united states and northern mexico these data reveal that isotopic signatures of turquoise deposits vary geographically according to regional and local differences in the geologic settings of turquoise mineralization as an archaeological case study we also report pb and sr isotopic data on 10 turquoise artifacts recovered from three late pre hispanic ca a d 1250 1400 ancestral zuni sites located in the el morro valley of western new mexico these have isotopic signatures uniquely consistent with the turquoise deposits of the cerrillos hills a location identified in zuni traditional history as an ancient source of turquoise these data thus establish pb and sr isotopic measurements as powerful tools for determining the sources of turquoise artifacts and provide a new framework for evaluating the role of turquoise in pre hispanic exchange networks across north america

isotopic and paleomagnetic constraints on the mesozoic tectonic evolution of south china in order to better constrain the paleogeographic evolution of south china we measured sm nd and rb sr isotopic compositions for 23 mesozoic granites that crop out throughout the area tightly grouped neodymium depleted mantle model ages 1 4 0 3 ga suggest the region is underlain by relatively homogeneous proterozoic crust and fail to define crustal provinces neither the isotopic nor geologic data suggest that a mesozoic suture exists however granites possessing anomalously high sm 8 ppm and nd 45 ppm concentrations relatively high initial epsilon neodymium 4 to 8 and high but variable initial 87sr 86sr 0 759 to 0 713 form a northeast trending zone that coincides with two prominent mesozoic basins southeast of the zone lie the majority of mesozoic intrusives and upper triassic to lower cretaceous extensional basins found in south china mesozoic paleomagnetic poles are well clustered northwest of the zone pre cretaceous poles southeast of it are discordant with respect to those from the northwest the only recognized tectonostratigraphic terrane in south china lies southeast of the zone the terrane is bordered by a northeast trending sinistral fault that was active in the mesozoic other faults in south china have similar attitudes ages and sense of shear together the observations suggest that the mesozoic tectonic regime in south china consisted of strike slip activity plus concomitant rifting as terranes or fragments of similar crust were transported north along sinistral faults the zone defined by the granites enriched in nd and sm demarcates displaced terranes to the southeast from relatively stable land to the northwest

a chemical and isotopic study of the laramide granitic belt of northwestern mexico identification of the southern edge of the north american precambrian basement along the laramide belt of northwestern mexico granitic rocks of similar bulk composition show isotopic and trace element signatures that help to delineate the position of the southern edge of the north american precambrian basement in the northern part the laramide plutons the northern granites intruded proterozoic crystalline rocks and a thick late proterozoic through paleozoic miogeoclinal cover of north american affinity in the central part the granitic bodies the central granites were emplaced into a sequence of paleozoic eugeoclinal rocks overlain by late triassic clastic units the southern part of the belt the southern granites intruded a less known crust characterized by middle to late mesozoic island arc related volcanic and sedimentary rocks of the guerrero terrane data from a suite of metaluminous to slightly peraluminous calc alkalic granitic rocks along the belt display north to south geochemical and isotopic variations which could correlate with the type of intruded basement the northern and central granites are characterized by strongly fractionated light rare earth element ree enriched patterns which display generally pronounced negative europium anomalies whereas the southern granites have lower total ree enrichments and much flatter chondrite normalized slopes displaying almost no europium anomalies isotopic results also suggest regional variations as shown by the following initial sr and end ranges 0 7070 to 0 7089 and24 2 to25 4 respectively for the northern granites 0 7060 to 0 7079 and23 4 to25 1 for the central granites and 0 7026 to 0 7062 and20 9 to 14 2 for the southern granites on the basis of their isotopic similarities the proterozoic mafic to intermediate lower crust revealed by xenoliths from young volcanic flows in southern arizona and northern mexico is interpreted as a reasonable parental source for the northern and central granites however mantle derived melts are not excluded the more primitive southern granites are interpreted to come from a source that lacked proterozoic basement instead they were probably derived by mixing of juvenile mantle melts with partial melts of the lower parts of the guerrero terrane in general the north to south compositional variations of the laramide granitic rocks of northwestern mexico reflect the crustal structure underneath the batholiths the sr and nd data indicate that the edge of the north american precambrian basement extends approximately southeastward from the coastal batholith of central sonora then about 200 km south of hermosillo in southern sonora the edge bends eastward and continues to the east beneath the sierra madre occidental volcanic province

multiphase magma intrusion ore enhancement and hydrothermal carbonatisation in the siah kamar porphyry mo deposit urumieh dokhtar magmatic zone nw iran abstract the siah kamar mo deposit skmd is located at the northwestern termination of the urumieh dokhtar magmatic zone and it is the only porphyry mo ore reserve in iran the exploration program documented 39 2 mt proved reserves 539 ppm mo and 66 4 mt probable reserves 266 ppm mo in this study field and petrographic investigations integrated with geochemical fluid inclusion and quartz chemistry and geochronological u pb zircon re os molybdenite and rb sr multimineral isochron studies are used to propose a metallogenic model for the mo mineralisation in the skmd the geology of the skmd is characterized by the emplacement of a multiphase oligocene basic intermediate at ca 33 30 ma to acidic 29 28 ma magmatic suite which intruded the eocene volcanic country rocks the alteration zone about 4 3 km in size and with a general nw se trend is centered within the main basic porphyry stock grading from an inner potassic sodic zone to peripheral phyllic propylitic halos the late acidic magmatic products stocks and dykes intruded and post dated the main alteration zone two stage mo mineralisation is recognised including i stage 1 disseminated molybdenite coeval with the formation of potassic sodic alteration and minor microscale fsp bt qz po veinlets and ii stage 2 high grade molybdenite carbonate sericite structurally controlled stockwork veining fluid inclusion systematics combined with titaniq thermometry documents a mineralising fluid system compatible with a transition from high temperature up to ca 600 c magmatic to epithermal 250 c conditions during progressive cooling exhumation and mixing with meteoric sources at shallow crustal conditions ca 7 3 km the re os molybdenite dating constrains the high grade mo ore formation at ca 29 28 ma attesting for the intimate linkage between the main mo mineralisation and the acidic magmatic phase in the area the rb sr geochronology of the potassic sodic alteration zones confirms the two stage magmatic mineralisation scenarios overlapping within errors with the results obtained from the u pb zircon geochronology and constraining the formation of the potassic sodic and phyllic alteration at ca 33 and 28 ma respectively our results document an uncommon scenario of two stage porphyry mo mineralisation associated with intensive late stage carbonate precipitation and achieved during a long lasting and multiphase magmatic pulses of oligocene age we highlight the dominant role of acidic fluid neutralisation for further ore enrichment during polyphase magma intrusion as the dominant factor controlling the mo mineralisation in the skmd comparison at a regional scale indicates that parameters such as longevity of magma supply progressive magma crystallization differentiation and the presence of a possible pre enriched crustal material should be considered responsible for the mo endowment in the udmz

the structural architecture of the footwall to the main uralian fault southern urals abstract the uralide orogen is a linear collisional belt formed during the upper paleozoic as a result of convergence between the east european craton and outboard terranes and accretion of intervening island arcs and obduction of oceanic crust onto the east european craton this paper presents a new structural subdivision of the southern urals to the west of the main suture zone that puts this part of the mountain belt in a context similar to that of other collisional orogenic belts this subdivision consists of a west vergent thrust stack that is made up of an autochthonous to parautochthonous foreland basin and a parautochthonous foreland thrust and fold belt flanked to the east by a metamorphic thrust stack the latter units are structurally overlain by allochthonous rocks of an accretionary complex slope sediments oceanic crust and high grade eclogite blueschist bearing gneiss where possible these units are defined on the basis of their internal stratigraphy and structure and on the nature of their bounding faults

slump structures in the late tertiary of the porcupine basin offshore ireland abstract a large late tertiary slump complex from the porcupine basin offshore western ireland is described it occurs in deep water probably mud prone sediments on the south west margin of a thermal subsidence basin overlying a pre cretaceous synrift succession the slump consists of head body and toe regions each with diagnostic internal characteristics the head region contains extensional features whereas the toe region suffered compression the main body acted as a relatively rigid unit in the southern zone of the slump complex while in the north it suffered gravity driven internal duplex thrusting a series of elongate channels infilled with material eroded from the crestal parts of the toe and body regions comprise a prominant chute zone local reworking of the basinward edge of the toe region also occurred a period of local turbidite deposition towards the centre of the basin appears to be coeval with the slumping the slump movement was probably influenced by a complex combination of fault induced earthquake movement facies and slope variations and by the local presence of an overpressured mud horizon which acted as a decollement surface

paleoconvergence rates determined from k2o sio2 ratios in magmatic rocks and their application to cretaceous and tertiary tectonic patterns in southwestern north america spatial temporal and chemical data may be used to calculate paleodip angles for paleosubduction zones assuming the position of the paleotrench is reasonably well known in turn paleoconvergence rates may be calculated according to the equation developed by luyendyk 1970 that relates dip angle to convergence rate data from cretaceous tertiary magmatic rocks indicate paleoconvergence rates of 7 to 8 cm yr for the period 130 to 85 m y ago convergence rates markedly increased to an average of about 14 cm yr for the period 85 to 45 m y decreased convergence rates are indicated from 45 to 20 m y paleoconvergence rates determined from magmatic rocks are generally in agreement with those determined independently by other workers from paleomagnetic data on ocean floor rocks the anomalously high rates of convergence determined from the igneous rock data may be due to subduction of younger more buoyant oceanc crust after 65 m y b p although recent observations from independent data suggest that eocene convergence may have been a high 20 to 26 cm yr paleomagnetically the period of constant convergence constant dip subduction from 130 to 85 m y ago correlates almost exactly with the long cretaceous normal polarity interval as suggested on the new lowrie alvarez 1981 geomagnetic time scale in contrast the post 85 m y period of variable convergence and variable dip subduction correlates with polarity events of short duration and frequent reversal tectonically the period of constant convergence rates from 130 to 85 m y ago correlates with sevier orogeny in nevada and utah the period of increased convergence from 85 to 45 m y ago correlates with classic laramide orogeny in wyoming and colorado the period of decreased convergence from 45 to about 20 m y ago correlates with a poorly understood and incompletely defined mid tertiary orogenic event

extensional shearing deformation and kilometer scale a type folds in a cordilleran metamorphic core complex raft river mountains northwestern utah cordilleran metamorphic core complexes are characterized by ductile mylonitic deformation and regional stretching lineations in the raft river mountains a mylonitic zone and a late superimposed detachment fault separate precambrian crystalline and metasedi mentary basement rocks from an upper plate made of allochthonous paleozoic rocks which suffered a brittle extensive deformation we suggest that the mylonitic ductile deformation is the result of tertiary extensional tectonics strain analysis shows that 1 strain results from large scale progressive shearing deformation in a non coaxial regime 2 e w regional stretching lineations represent the direction of shearing and transport 3 shear criteria indicate an east directed movement 4 strain magnitude is increasing eastward 5 kilometer scale folds parallel to the lineations are interpreted as a type folds formed by eastward shearing of a previously northward dipping layering measurement of striated faults in the upper plate gives an e w direction of extension parallel to the lineations thus ductile and brittle deformations are closely related to the same regional scale extensional tectonics a model is proposed to explain the observed geometry and kinematics of the structures the mesozoic to paleocene cordilleran compressional tectonics induced an overthickening of the crust in the hinterland belt at the future emplacement of the complexes important uplift abnormal heating and granite emplacement occurred later during the collapse of the former belt the combined effects of thermal and gravitational instabilities during tertiary extensional tectonics enabled the development of a ductile shear zone localized at the precambrian basement paleozoic cover interface the brittle extension of the upper crust is displaced laterally along this flat shear zone and transformed farther east into the extended regions of the middle and lower crust

metamorphic terranes isotopic provinces and implications for crustal growth of the western united states simplified maps of the western cordillera indicating distribution of metamorphic facies and times of principal recrystallization have been compiled despite rearrangement by transcurrent shuffling general trends are recognizable narrow belts of phanerozoic high p blue schist and serpentinized peridotite lie outboard from broad penecontemporaneous high t metamorphosed calcalkaline magma intruded belts bordering the pacific ocean and both are disposed approximately parallel to the present day north american margin they represent recrystallized products of mid paleozoic and younger subduction zones andean type margins and exotic island arcs in contrast dominant metamorphic mineral parageneses within the continental interior are spatially associated with chiefly mesozonal granitic plutons glaucophane schists eclogites and large tracts of ophiolitic ultramafics are absent in part due to selective overprinting of old accretionary margin lithotectonic assemblages by subsequent orogenies high t recrystallization and anatexis for example at depth within the california coast ranges high p phases are currently being destroyed farther inland a general paucity of oceanic petrotectonic assemblages is evident possibly reflecting the differential sinking of dense basaltic peridotitic units during thermal softening preserved metamorphic field gradients reflect the magnitude of subsequent uplift and erosion as well as original pt conditions late mesozoic to mid cenozoic recrystallization accompanied earlier crustal thickening ductile deformation succeeded by later extension brittle faulting mylonitization mesozoic cenozoic metamorphism involved cratonal rocks in the mojave sonoran desert but in nevada and to the north eugeoclinal sections were recrystallized metamorphic intensity decreases eastward toward the phanerozoic hinge line basement rocks in the rockies display the effects of shallow level crustal deformation but much less widespread evidence of post proterozoic plutonism and regional metamorphism initial pb nd and sr isotopic compositions and crystallization ages of igneous rocks in comparison with times of intrusion recrystallization and metamorphic facies distributions are compatible with a geologic scenario involving gradual proximal growth of the ancient continent chiefly southward from the archean wyoming craton during early and mid proterozoic time followed by late proterozoic phanerozoic westward development accretion involved the incorporation of some exotic mostly oceanic outboard terranes however continental growth in the western u s cordillera during both proterozoic and phanerozoic time periods appears to have been due chiefly to partial fusion and magma ascent above subducting paleo pacific lithospheric plates combined with metamorphic sedimentary reworking in the forearc trench back arc setting rather than resulting from the amalgamation of preexisting ancient continental fragments

nd and sr isotope chronostratigraphy of colorado plateau lithosphere implications for magmatic and tectonic underplating of the continental crust nd sr isotopes and major and trace element abundances were measured in lower and upper crustal xenoliths carried in tertiary minettes and kimberlitic diatremes of the colorado plateau the objective was to establish the vertical distribution of mantle extraction ages for an undisturbed precambrian crustal province characterized by normal thickness and low cratonic heat flow and to thereby evaluate the importance of magmatic or tectonic underplating in crustal growth mid proterozoic age 1 7 2 0 ga material is found at all levels of the crust although mafic granulites and amphibolites have major and trace element compositions compatible with an origin as magmatically underplated material nd model ages do not indicate that there has been significant mantle contribution to the lower crust by igneous processes such as magmatic underplating since the main crust forming event ca 1 85 ga ago the meta igneous lower crustal xenoliths have relatively radiogenic nd isotopic compositions and unradiogenic sr compositions there is little variability in nd model ages in spite of large variability in sm nd high and variable sm nd ratios were therefore established early in the history of the protolith during igneous or metamorphic processes coincident with or shortly after extraction from the mantle metapelitic xenoliths tectonically emplaced into the lower crust have the same proterozoic model ages as meta igneous parts of the lower crust these paragneisses are probably arc associated sediments that were underthrust during terrane accretion in the proterozoic the isotopic data indicate that eclogite xenoliths are likely to represent proterozoic lithosphere rather than subducted mesozoic morb as previously proposed a number of the eclogite xenoliths have experienced a metasomatic event which introduced lree sio2 and na2o and shifted the nd and sr isotopic compositions the least altered eclogite xenoliths have major and trace element and radiogenic nd isotopic compositions similar to those of other proterozoic mafic lower crustal xenoliths a more plausible protolith for the eclogites is proterozoic lithosphere that was metamorphosed to eclogite facies conditions either during precambrian continental assembly or in more recent times

nd sr and o isotopic study of the petrogenesis of two syntectonic members of the new hampshire plutonic series nd sr and o isotope systematics were used to investigate the petrogenesis of two adjacent plutons of the bethlehem gneiss bg and the kinsman quartz monzonite kqm exposed within the central maine terrane cmt of new england both are acadian aged 413 ma synmetamorphic and syntectonic members of the new hampshire plutonic series nhps potential source rocks analyzed for this study include silurian and devonian metasedimentary rocks of the cmt and ordovician metasedimentary rocks and granitic gneisses of the bronson hill anticlinorium bha which border the cmt to the west the sr 413 nd 413 and 18o values for the kqm range from 56 3 to 120 0 2 8 to 6 4 and 7 6 to 12 9 respectively values for the bg range from 7 4 to 144 7 0 6 to 9 3 and 8 3 to 11 3 respectively and values for possible source rocks range from 38 1 to 654 2 10 7 to 5 4 and 6 2 to 14 1 respectively both the bg and kqm have extremely heterogeneous initial isotopic compositions consistent with mixing of multiple crustal source rocks and neither contains a volumetrically significant i e 10 mantlederived component overlapping values of nd 413 sr 413 and 18o values for both the bg and kqm samples resemble values for metasedimentary host rocks of the cmt and bha we observe no systematic correlations between nd and sr values for either the bg or the kqm the sr and 18o values for the bg do not form any simple mixing trends nor is there any direct correlation between the isotopic compositions of contact bg samples and their adjacent host rocks in contrast to our observations for the kqm lathrop et al 1994 we propose that the kqm and bg magmas were generated through anatexis of metasedimentary rocks from both the bha and cmt in response to crystal thickening during the acadian orogeny melting may have been initiated within cmt metasediments in response to high heat production in these mid crustal rocks combined with crustal thickening whereas melting of bha rocks with normal crustal heat production which were located at lower crustal levels than cmt rocks is likely to have been driven by crustal thickening alone following upward advection of mobile bha magmas bha and cmt derived magmas may have mingled during complex acadian deformation in the cmt thus accounting for the isotopic similarities we observe between the bg and the kqm

zircon u pb and molybdenite re os dating and geological implications of the shimadong porphyry molybdenum deposit in eastern yanbian northeastern china the shimadong porphyry mo deposit is located in eastern yanbian in the eastern part of the north margin of the north china craton northeastern china here we present the whole rock major and tra

early paleozoic island arc accretion to the north china craton and the shang dan fault zone a major paleoplate boundary in eastern asia the early paleozoic tectonic evolution of part of the qinling dabie shandong orogenic belt is reconstructed on the basis of the results of field mapping geochemical and geochronological studies the qinling orogenic belt separates the archean proterozoic north china craton ncc from the south china craton scc also yangtze craton the study area is located about 90 km southwest of the city of xi an three lithologically distinctive zones separated from each other by fault zones can be distinguished passive continental margin deposits of the ncc zone 1 have end t values between 6 16 and 12 54 and tdm ages between 1 29 and 2 20 ga they are separated from an early paleozoic island arc sequence zone 2 by the sinistral chenche fault mafic volcanic lithologies in the southern part of zone 1 are associated with the development of a passive continental margin in late proterozoic time similiar lithologies of zone 2 have geochemical characteristics of an oceanic island arc accretion was accompanied by a strong deformation event between early ordovician and late silurian time magmatic intrusions in zone 2 and the southern part of zone 1 are associated with a short lived magmatic arc that developed above a north dipping subduction zone on the modified continental margin of the ncc in late silurian to early devonian time the end t values of felsic intrusions from the northern part of zone 2 decrease in a northern direction from 1 78 to 1 05 mafic to intermediate intrusions in the southern part of zone 2 have positive end t values from 1 28 to 2 04 as well as low 87sr 86sr i values between 0 705 and 0 706 indicating an increasing mantle component toward the south low grade metamorphic pelites are separated from the island arc sequence of zone 2 by a 2 km wide shang dan shear zone isotopic studies show strong similarities between a granite sample from zone 3 and samples from the scc 87sr 86sr i values increase from 0 709 to 0 713 whereas end t values decrease from 1 90 to 5 34 in a southern direction the shear zone that separates zone 2 from 3 is of fundamental importance and marks the boundary between the ncc and the scc the results presented in this paper document a previously unknown early paleozoic tectonic evolution of the qinling orogenic belt and delineate one of the fundamental paleoplate boundaries in eastern asia

identifying multiple detachment horizons and an evolving thrust history through cross section restoration and appraisal in the moine thrust belt nw scotland abstract many thrust systems including parts of the moine thrust belt are commonly interpreted as rather simple imbricate fans splaying from a master detachment floor thrust at depth we use field observations and geological map data to construct cross sections through the achnashellach culmination southern moine thrust belt northwest scotland to test this interpretation initially cross sections are constructed by assuming a single lower detachment line length imbalances and thrust trajectory mismatches between deformed and restored state sections indicate an invalid model significant differences in horizon lengths between two rock units are seen indicating the position of a second detachment which when incorporated into the deformed state cross section creates a valid structural model the presence of this second detachment accounts for complex geometries seen at outcrop and indicates that the achnashellach culmination is likely to have formed by the sequential activation of two detachment horizons this new structural model has been derived using an iterative workflow involving cross section construction section balancing and integration of field observations from across the study area ensuring model validity in three dimensions this workflow is applicable to other systems in general

crustal affinities of metallogenesis in the american southwest the source of metals in many lands of ores and ore deposit styles remains uncertain notwithstanding more than a century of field studies scientific advances in concepts and enhancement of analytical capability however numerous geologic research efforts that have addressed many relevant themes in southern arizona have resulted in different kinds of data supporting and consistent with the interpretation of significant association of some ore metals of this region with cratonic crust these themes range in scale from studies of regional geology geophysical interpretations and precious metal production through petrology to trace element and isotope geochemistry the notion of a crustal source for metals contrasts with many long standing ideas of direct mantle sources for this metal province or more recently direct derivation of metals from subducted materials a hundred years of recorded silver and gold production reveal a two fold separation of mining districts in arizona and new mexico on the basis of ranges of produced ag au ratio that correspond in turn with a separation of two distinct geologic domains of the southern cordilleran metal province the produced ag au ratio in districts of different ages ore styles tectonic setting and metal habit are not affected by deposit style or ore control or igneous rock type or vertical zoning and weathering studies of the isotopes and trace element chemistry of related igneous rocks reveal that ore related intrusions have a significant crustal progenitor studies of pb and os isotopes have discovered strong signals of crustal parentage in ore minerals the regional geology metallization history production and chemical and isotopic data strongly support a hypothesis of crustal sources of some of the metal in this large and complex province

excursus on gravity gliding and gravity spreading abstract the terms gravity gliding and gravity spreading have long been used to describe deformation driven by gravity alone however the traditional definitions of these terms cannot be applied unambiguously in many situations the primary difficulties arise because rocks are not ideally rigid detachment surfaces may not be planar substrates may be deformable and rock bodies do not deform in isolation the term gravity spreading is still useful if it is simply defined as gravity driven lateral extension and vertical contraction regardless of basal slope and coherence of the body i suggest that the term gravity gliding should be used rarely and only if the defining characteristics are clearly stated and understood in most cases more detailed descriptions should be used instead of or in addition to either of these terms to capture the behavior of rock masses deforming under gravity

age and origin of base and precious metal veins of the coeur d alene mining district idaho ore bearing quartz carbonate veins of the coeur d alene mining district yield 87sr 86sr ratios of 0 74 to 1 60 for low rb sr carbonate gangue minerals similar to current ranges measured in middle proterozoic high rb sr rocks of the belt supergroup stable isotope and fluid inclusion studies establish a genetic relationship between vein formation and metamorphic hydrothermal systems of the region these extraordinary 87sr 86sr ratios require accumulation of radiogenic 87sr in a high rb sr system over an extended period prior to incorporation of sr into the hydrothermal veins evaluation of the age and composition of potential sources of highly radiogenic sr indicates that the ore bearing veins of the coeur d alene district formed during the cretaceous from components scavenged from rocks of the belt supergroup the primary host rocks of the district proterozoic pb isotope ratios observed in galena from many coeur d alene veins were established when pb separated from uranium during deposition or diagenesis of the belt supergroup at 1400 to 1500 ma possibly as disseminated syngenetic deposits k ar and rb sr apparent ages and 18o values of belt supergroup rocks decrease from the coeur d alene district toward the idaho and kaniksu batholiths approximately normal to the trends of metamorphic isograds fold axes foliation and the major reverse faults of the district isoclinal folding thrust faulting high temperature metamorphism granitic plutonism and regional scale metamorphic hydrothermal activity is documented in the region between 140 and 45 ma representing the only such combination of events in the coeur d alene region subsequent to about 1300 ma the sr and oxygen results and geologic evidence favor formation of the ore bearing carbonate veins by fluids related to a complex metamorphic hydrothermal system during the cretaceous pb with proterozoic isotopic compositions was probably mobilized and incorporated like other metals into the hydrothermal veins during this event the ore bearing veins were sheared and displaced during early tertiary northwest trending dextral strike slip faulting along the osburn fault and related structures of the lewis and clark line

triggers for the formation of porphyry ore deposits in magmatic arcs porphyry ore deposits supply much of the copper molybdenum gold and silver used by humans a review of the main processes that trigger porphyry ore formation suggests that sulphide saturation of the magmas that supply the metals could be the overriding mechanism that helps control the temporal and spatial distribution of the ore deposits

calcium isotopes in igneous rocks and the origin of granite abstract the k ca radioactive parent daughter system provides a tool for tracing the origins of igneous rocks it is complementary to other isotopic systems because as stoichiometric constituents of major minerals the concentrations of k and ca and the k ca ratio in rocks are simply related to mineralogy in this paper we report the first high precision calcium isotopic analyses of continental granitic rocks island arc rocks and mid ocean ridge basalts these data show that mid ocean ridge basalts have the low 40 ca 42 ca ratios expected for the earth s mantle but that island arc rocks have slightly higher 40 ca 42 ca ratios indicative of crustal calcium in their magma sources many granitic rocks have high initial 40 ca 42 ca ratios and in conjunction with independent evidence for the age of the crustal sources these ratios provide constraints on the k ca ratios and in turn on the silica contents and residual mineralogy of the deep crustal magma sources