unexposed archean components and complex post archean accretion reworking processes beneath the southern yangtze block revealed by zircon xenocrysts from the paleozoic lamproites south china abstract integrated u pb dating and hf isotope analysis of zircon xenocrysts from the baifen lamproites of the zhenyuan area in the southeastern guizhou province offer a unique glimpse into the evolution of the deep continental crust beneath the southern part of the yangtze block south china a total of 148 zircons with 90 110 concordance yield u pb ages varying from 3458 9 ma to 252 2 ma they generally have high th u ratios 0 3 indicating a magmatic origin the two youngest magmatic zircons give a weighted mean 206pb 238u age of 253 0 2 8 ma which is interpreted as the emplacement age of the host baifen lamproites most zircons with pre eruption ages are xenocrysts derived from the deeper crust of the southern yangtze block they define two major paleoproterozoic age populations at 2 17 ga and 1 8 ga with similar hf model ages tcrust of 2 4 2 8 ga peak at 2 64 ga the oldest zircon has a 207pb 206pb age of 3458 9 ma with ehf t 1 47 and tcrust 3 7 ga this demonstrates the presence of archean crustal components or remnants as old as 3 7 ga beneath the southern yangtze block magmatic events involving significant addition of juvenile mantle derived materials mainly occurred at 2 2 2 1 ga and 2 0 1 8 ga but the latter event also involved reworking of the neoarchean crust and might represent the cratonization of the yangtze continent during the middle paleoproterozoic which could be correlated to the assembly of the columbia supercontinent this segment of the yangtze block became tectonically quiescent until 1 2 ga implying that the crustal stabilization lasted for ca 600 million years a few late mesoproterozoic zircon xenocrysts within the age range 1 3 1 0 ga suggest the occurrence of grenville aged events these neoproterozoic zircon xenocrysts 992 547 ma have a wide range of ehf t values 8 47 to 22 07 consistent with the zircon hf isotopic compositions of widespread coeval igneous rocks in the yangtze block the data show that the yangtze block has undergone important crustal growth and reworking during the neoproterozoic in response to the breakup of the rodinia supercontinent the early middle paleozoic zircon xenocrysts 513 357 ma have negative ehf t values 2 97 to 12 69 and tcrust hf model ages of 1 59 2 27 ga indicating reworking of the precambrian crustal basement without juvenile contributions during the caledonian orogeny the positive ehf t values 13 79 to 0 22 of twelve late paleozoic zircons 284 264 ma with a major age peak at ca 275 ma suggest that the precambrian basement beneath the southern yangtze block experienced an episode of strong rejuvenation during the permian we propose a possible linkage between the baifen lamproite magmatism 284 252 ma and the emeishan flood basalt volcanism

tectonothermal evolution of the mayuan assemblage in the cathaysia block implications for neoproterozoic collision related assembly of the south china craton the mayuan assemblage in the cathaysia block southeast china consists of felsic paragneiss pelitic schist greenschist amphibolite marble calcsilicate and quartzite that underwent three episodes of deformation d1 d3 and four episodes of metamorphism m1 m4 in the early neoproterozoic the m1 assemblage consists of mineral inclusions defining an early foliation s1 within porphyroblasts represented by chlorite muscovite biotite plagioclase quartz in pelitic schist and actinolite chlorite epidote albite quartz enclosed in amphibolite m2 coincides with the development of the regional schistosity s2 and represents the formation of the porphyroblasts and growth of matrix minerals resulting in development of prograde metamorphic zones chlorite biotite garnet staurolite and kyanite zones m3 is simultaneous with the third phase of deformation d3 and produced sillimanite bearing mineral assemblages in pelitic schist and hornblende bearing assemblages in amphibo lite the last metamorphic episode m4 gave rise to the retrogressive assemblage chlorite muscovite in pelitic rock and actinolite chlorite epidote in amphibolite the sequence of mineral assemblages and history of metamorphic reactions built from the petrogenetic grid of pelites suggest a near isothermal decompression clockwise p t path for the mayuan pelitic schists using the tweequ software program the garnet biotite thermometer and garnet muscovite biotite plagioclase barometer yield p t conditions for m1 of 5 5 to 6 0 kb and 450 to 500 c and conditions for the garnet staurolite and kyanite zones of m2 of 6 0 to 7 0 kb and 550 to 600 c 6 0 to 7 5 kb and 600 c and 11 0 to 11 5 kb and 600 c the p t conditions of m3 were estimated at 570 to 625 c and 4 0 to 4 5 kb using the muscovite biotite thermometer and hornblende plagioclase geothermo barometer the garnet chlorite thermometer yields temperatures of 300 to 400 c for m4 but the pressures of m4 cannot be quantitatively estimated because of the lack of a suitable geobarometer these p t estimates also define an near isothermal decompression clockwise p t path which is involved in initial crustal thickening followed by rapid exhumation and final cooling and is related to amalgamation of the cathaysia and yangtze blocks to form the south china craton

petrology and ion microprobe u pb chronology applied to a metabasic intrusion in southern sweden a study on zircon formation during metamorphism and deformation the aker metabasite occupies a key position in a major tectonic lineament in southernmost sweden the protogine zone which coincides closely with the eastern boundary of the late mesoproterozoic sveconorwegian orogen of southwest scandinavia metamorphic reactions associated with the transformation from isotropic gabbro to foliated garnet amphibolite were identified from disequilibrium textures of which some involved release of zirconium zr and growth of metamorphic zircon ion microprobe dating of igneous zircon gave 1562 6 ma whereas metamorphic zircons yielded ages of 1437 21 1217 75 and 1006 68 ma the presence of baddeleyite pseudomorphs made up of saccharoidal zircon and a higher abundance of older rather than younger metamorphic zircons suggest redistribution of zr into new zircon first by the breakdown of baddeleyite zro2 and later by the consumption of igneous phases containing trace amounts of zr several generations of metamorphic zircon and the presence of 1 56 and 1 22 ga mafic intrusions along the protogine zone call for a complex tectonic history probably reaching back to at least similar to1 56 ga growth of metamorphic zircon at similar to1 44 ga may relate to a regional compressional event the wnw trending deformational structures on both sides of the protogine zone may possibly relate to that event the similar to1 22 ga metamorphic zircons are coeval with the emplacement of numerous granitic syenitic and mafic intrusions along and parallel to the protogine zone the age around 1 0 ga finally marks sveconorwegian metamorphism for which thermobarometry of the aker garnet amphibolite suggests 1000 1200 mpa at 600degreesc 630degreesc thereafter significant relative uplift of the rocks to the west of the protogine zone occurred on nearly vertical north south trending deformation zones less

petrogenesis and tectonic implications of early cretaceous s and a type granites in the northwest of the gan hang rift se china the gan hang rift trending at least 450 km in a ne sw direction is a part of a mesozoic basin and range province in southeastern china detailed shrimp zircon u pb chronology major and trace element and sr nd hf isotope data of three granitic plutons and a diabasic dike in the northwest of the gan hang rift are used to explore the origin of these granites and their relationship to the evolution of the gan hang rift shrimp zircon u pb dating shows that the granitic plutons and diabasic dike were emplaced in the early cretaceous 122 129 ma the tongshan and damaoshan plutons close to the gan hang rift consist mainly of weakly peraluminous granitic rocks which show a2 subtype affinity these granites have initial 87sr 86sr ratios of 0 7080 0 7103 end t values of 1 4 to 5 6 and ehf t in situ zircon values of 3 8 to 1 2 detailed elemental and isotopic data suggest that they were formed by partial melting of granulitized mesoproterozoic metamorphic basement including metasedimentary and metaigneous rocks in the shallow 30 km crust at a high temperature 823 c these pure crustal melts underwent crystal fractionation of biotite plagioclase and k feldspar forming the more felsic end member of granitic rocks the ehu pluton more distant from the gan hang rift is composed of two mica granites which are strongly peraluminous and are s type granites these granites have higher initial 87sr 86sr ratios 0 7162 0 7191 and lower end t 7 1 to 7 4 and ehf t 6 8 in situ zircon values than the tongshan and damaoshan granites detailed elemental and isotopic data suggest that the ehu granites were formed by partial melting of paleoproterozoic metasedimentary basement in the deep 40 50 km crust at a relatively low temperature 757 c with no fractional crystallization and mantle derived magma mixing in their evolution the coeval diabasic dike is calc alkaline and has initial 87sr 86sr ratio of 0 7085 end t value of 0 9 and ehf t in situ zircon value of 7 1 suggesting that it was derived from the asthenospheric mantle wedge that had been metasomatised via addition of subducted sediment derived melt with monazite in the residual phase the association of early cretaceous 122 129 ma s and a type granites in the northwest of the gan hang rift marks the onset of back arc extension or intra arc rift with ongoing extension the crust and lithospheric mantle became progressively thinned the upwelling of asthenosphere triggered partial melting of both metasedimentary and metaigneous rocks in the more thinned crust close to the gan hang rift forming the a type granitic magmas such as tongshan and damaoshan whereas partial melting of metasedimentary rocks in the less thinned crust farther from the gan hang rift formed the s type granitic magmas such as ehu the red sediments with the total thickness more than 10 000 m have been successively deposited in the gan hang rift valley since the late early cretaceous 105 ma suggesting that this region experienced the most back arc extension

ordovician appinites in the wugongshan domain of the cathaysia block south china geochronological and geochemical evidence for intrusion into a local extensional zone within an intracontinental regime abstract palaeozoic mafic igneous rocks are potentially significant in constraining the tectonic nature and evolution of the kwangsian orogeny in the eastern south china block yet they have received little attention because of their limited outcrop geochemistry and geochronology was carried out on newly identified ordovician ultramafic mafic appinites in the wugongshan domain of the cathaysia block seven appinite samples yielded 206pb 238u crystallisation ages ranging from 452 4 ma to 473 3 ma abundant 480 500 ma zircon xenocrysts and or inherited zircons were found in the appinites possibly indicating an earlier magmatism episode in the early palaeozoic period the wugongshan appinites are ultramafic to mafic in composition and the ultramafic rocks display features of cumulates high concentrations of mgo fe2o3t cr ni and low concentrations of total alkali and total rare earth elements ree the appinite geochemistry displays relatively flat chondrite normalised ree patterns with slight enrichment in light ree and weak negative eu anomalies enrichment in large ion lithophile elements such as rb k and weak depletion in nb ta in primitive mantle normalised trace element patterns we suggest that the wugongshan appinites likely originated from an ancient metasomatised mantle and that crustal assimilation fractional crystallisation afc magma mingling and hydration were involved in the petrogenetic process based on the combination of geochemistry crust like bulk sr nd and zircon hf isotopic compositions end t 8 2 to 3 2 initial 87sr 86sr ratios of 0 7067 0 7144 zircon ehf t values peaking at 9 to 3 and regional geological data further considering the alignment and chronology of the appinites we suggest that the appinitic magmas probably were emplaced along the jiangshan shaoxing fault in a local extensional zone in an intracontinental regime in the early palaeozoic

petrogenesis of granitoids and associated xenoliths in the early paleozoic baoxu and enping plutons south china implications for the evolution of the wuyi yunkai intracontinental orogen abstract the early paleozoic wuyi yunkai orogen was associated with extensive felsic magmatic activities and the orogenic core was mainly distributed in the yunkai and wugong domains located in the western cathaysia block and in the wuyi domain located in the central part of the cathaysia block in order to investigate the evolution of the wuyi yunkai orogen elemental and sr nd isotopic analyses were performed for granites from the baoxu pluton in the yunkai domain and from the enping pluton in the central part of the cathaysia block the baoxu pluton consists of biotite granite with abundant xenoliths of gneissic granite granodiorite and diorite and the enping pluton is mainly composed of massive granodiorite biotite granites 441 5 ma and gneissic granite xenolith 443 4 ma of the baoxu pluton are all weakly peraluminous a cnk 1 05 1 10 they show high sr y and la yb ratios and have negative bulk rock end t values 7 0 to 4 4 which are similar to coeval gneissic s type granites in the yunkai domain and were probably derived from dehydration melting of a sedimentary source with garnet residue in the source granodiorites 429 3 ma from enping and granodiorite xenolith 442 4 ma from baoxu are metaluminous and have ree patterns with enriched light ree and flat middle to heavy ree possibly generated by the dehydration melting of an igneous basement at middle to lower crustal level diorite xenolith from baoxu is ultrapotassic k2o 4 9 wt has high contents of mgo 7 0 wt cr 379 ppm and ni 171 ppm and shows pronounced negative nb ta and ti anomalies this xenolith also has negative end t value 3 6 and low rb ba and high ba sr ratios and is thus interpreted to be derived from an enriched lithospheric mantle with the breakdown of phlogopite early paleozoic i and s type granites in the wuyi yunkai orogen mostly have negative end t values and do not have juvenile components consistent with genesis by an intracontinental orogenic event these early paleozoic granites occur near the ancient suture zone between the yangtze and cathaysia blocks and have high la yb and sr y ratios likely due to the existence of residual garnet in the source suggesting the thickened crust at ca 440 ma the 450 440 ma gneissic s type granites near the suture zone are earlier than those in the central part of the cathaysia block 430 ma the crustal thickening along the ancient suture zone at 440 ma propagated into the central part of the cathaysia block as evidenced by the 430 ma granites early paleozoic i type granites near the suture zone clearly show involvement of significant mantle derived materials in contrast to granites in the central part of the cathaysia block the ancient suture zone may have acted as channels for the emplacement of mafic magmas during the collapse of an intracontinental orogen

lower crustal granulite xenoliths from the pannonian basin hungary part 2 sr nd pb hf and o isotope evidence for formation of continental lower crust by tectonic emplacement of oceanic crust mafic granulite xenoliths from the lower crust of the pannonian basin are dominated by lree depleted bulk rock compositions many of these have morb like 143nd 144nd but 87sr 86sr is elevated relative to most morbs their 18o values cover a wide range from 3 8 to 9 5 a group of lree enriched mafic granulites have higher 87sr 86sr 0 704 0 708 and lower 143nd 144nd 0 5128 0 5124 with higher 18o values on average 7 8 to 10 6 than the lree depleted granulites the lree enriched granulites are however isotopically similar to newly discovered metasedimentary granulite xenoliths a sublinear correlation in ehf end isotope space has a shallower slope than the crust mantle array with the metasedimentary rocks forming the low ehf end member the radiogenic end is restricted to the lree depleted granulites and these overlap the field of morb pb isotopes for the lree depleted samples are less radiogenic on average than those of the lree enriched and metasedimentary xenoliths and metasedimentary granulites have consistently higher 208pb 204pb the wide range in 18o over a restricted range in nd and sr isotope values in combination with the predominance of lree depleted trace element compositions is consistent with an origin as a package of hydrothermally altered oceanic crust the existence of 18o values lower than average morb and or mantle peridotite requires that at least some of these rocks were hydrothermally altered at high temperature presumably in the oceanic lower crust the low 143nd 144nd of the lree enriched mafic granulites cannot be explained by simple mixing between a lree depleted melt and an enriched component represented by the recovered metasediments instead we interpret these rocks as the metamorphic equivalent of the shallowest levels of the ocean crust where pillow basalts are intimately intercalated with oceanic sediments a possible model is accretion of oceanic crustal slices during subduction and convergence followed by high grade metamorphism during the alpine orogeny

geochemistry of river borne clays entering the east china sea indicates two contrasting types of weathering and sediment transport processes the east china sea is characterized by wide continental shelf receiving a huge input of terrigenous matter from both large rivers and mountainous rivers which makes it an ideal natural laboratory for studying sediment source to sink transport processes this paper presents mineralogical and geochemical data of the clays and bulk sediments from the rivers entering the east china sea aiming to investigate the general driving mechanism of silicate weathering and sediment transport processes in east asian continental margin two types of river systems tectonically stable continental rivers and tectonically active mountainous rivers coexist in east asia as the direct weathering products clays can better reflect the silicate weathering regimes within the two river systems provenance rock types are not the dominant factor causing silicate weathering intensity difference existed in the east asian rivers the silicate weathering intensity of tectonically stable river basins is primarily driven by monsoon climate and the sediment transfer is relatively slow because of natural trapping process and increasing damming effect the geochemistry of these river borne sediments can thus indicate paleo weathering intensities in east asian continent in contrast silicate weathering intensity in tectonically active mountainous rivers is greatly limited by strong physical erosion despite the high temperature and highest monsoon rainfall the factors controlling silicate weathering in tectonically active catchments are complex and thus it should be prudent to use river sediment records to decipher paleoclimate change these two different silicate weathering regimes and sediment transport processes are manifestations of the landscape evolution and overall dominate the sedimentation in asian continental margin

geochronology and petrogenesis of pan african syn tectonic s type and post tectonic a type granite namibia products of melting of crustal sources fractional crystallization and wall rock entrainment abstract the oetmoed granite migmatite complex ogmc central damara orogen namibia consists mainly of 526 to 516 ma garnet and cordierite bearing granite and subordinate 488 to 494 ma hornblende and titanite bearing granite in the form of planar sheets and dykes additionally a slightly elongated granite body occurs in the center of the complex the garnet and cordierite bearing granite has major and trace element characteristics of s type granite but the hornblende and titanite bearing granite has higher hfse and ree contents similar to a type granite whereas the garnet and cordierite bearing granite contains numerous restitic xenoliths the hornblende and titanite bearing granite is xenolith free the country rocks are cordierite sillimanite k feldspar garnet bearing metasedimentary rocks and migmatite cordierite and garnet rich xenoliths in the s type granite do not represent primary restite their depleted chemical composition is best explained by varying and large degrees of partial melting of incorporated country rocks most chemical variations among the garnet and cordierite bearing granite can be explained by processes linked with fractional crystallization of plagioclase biotite and accessory phases mostly monazite and zircon major and trace element data and high 18 o values suggest that the least evolved members of the garnet and cordierite bearing granite were derived from metapelitic rocks at ca 800 c as inferred from monazite and apatite dissolution thermometry higher cao and na2o but lower sio2 contents and lower rb sr ratios as well as lower 18 o values of the hornblende and titanite bearing granite suggest that they are more likely generated by partial melting of non pelitic sources metagranitoids at temperatures in excess of 900 c decreasing tio2 na2o feotot mgo cao total ree content but increasing al2o3 and k2o indicate fractionation of mainly hornblende and titanite in the case of the hornblende and titanite bearing granite the differing compositions of the garnet and cordierite bearing granite and the hornblende and titanite bearing granite are attributed to different source rocks metapelite instead of metagranitoid and different temperatures during melting as inferred from accessory phase dissolution thermometry furthermore significant entrainment of country rock in some samples played a major role during petrogenesis of the garnet and cordierite bearing granite but was not important during the evolution of the hornblende and titanite bearing granite intrusion of such hot felsic magmas close to the inferred peak of metamorphism has probably caused in part the high temperature metamorphism and anatexis of the country rocks at relatively low pressures

diagenesis and reservoir quality of overpressured deep water sandstone following inorganic carbon dioxide accumulation upper miocene huangliu formation yinggehai basin south china sea abstract turbidite deposits overpressure hydrothermal fluid activity and co 2 accumulations are the basic geologic characteristics of the upper miocene huangliu formation sandstone reservoir in the dongfang gas field yinggehai basin this study aims to unravel the timing and origin of dissolution in sandstone and evaluate the effects of inorganic co 2 accumulation on reservoir quality a comparative study between area dfx 1 co 2 rich and area dfx 2 co 2 poor has illustrated the differences in diagenetic alteration and the effects of co 2 accumulation on the sandstone reservoir diagenetic alteration of sandstones in area dfx 1 was characterised by intense dissolution and medium cementation dissolution of silicates following inorganic co 2 charging in the dfx 1 area created a higher percentage of dissolution porosity 41 0 53 9 of total visible porosity compared with minor dissolution porosity in the dfx 2 area 16 7 29 6 of total visible porosity small amounts of kaolinite authigenic quartz ankerite and siderite were precipitated by co 2 water rock reactions in area dfx 1 these minerals are almost absent in area dfx 2 the carbonate cement of the huangliu formation sandstone in area dfx 1 is characterised by light 13 c 3 3 to 1 6 pdb which is consistent with formation from inorganic carbon the timing of dissolution by inorganic co 2 is suggested to be at about 0 4 ma based on the previous simulation experiments in the two areas studied overpressure was caused by pressure transmission along deep open faults and was not related to mudstone undercompaction overpressure did a little to contribute to porosity preservation co 2 accumulating at low partial pressures related to hydrothermal fluid flow cannot make a net increase in porosity in the huangliu formation sandstone of the dongfang gas field

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

thermal control on post orogenic extension in collision belts abstract intracontinental extension develops in two different ways in the rhine graben the baikal or the east african rifts it is localized in a long and narrow zone along a few normal faults which often delineate a single graben in contrast in the basin and range province or the tibetan plateau it is distributed over a much broader area up to more than 1000 km across this difference arises from differences in rheology and applied forces widespread extension probably reflects the thinning of a previously thickened crust geological observations indicate that only wide orogenic belts undergo late or post orogenic thinning a related fact is that anatectic granites seem to be most abundant in wide orogenic belts the general correlation between belt width and occurrence of both extension and anatectic granites suggest that it reflects in part the characteristics of horizontal heat transfer between thickened crust and surroundings in wide orogenic plateaux the large amount of heat produced in the crust by radioactive decay and lack of erosion leads to high temperatures in narrow mountain belts horizontal heat transfer and high erosion rates concur to prevent temperatures from rising to values at which the crust may yield in extension we have tested this hypothesis using transient two dimensional numerical models of orogenic belts focussing on the effects of the shortening rate the final width of the belt and the rate of crustal radiogenic heat production in the range of geological values the shortening rate has little influence on the results crustal temperatures increase as a function of belt width we find that the sensitivity of crustal temperatures to belt width is most pronounced in the 100 300 km width range and for large values of crustal heat generation the pressure temperature paths followed by geological formations depend on the belt width which is consistent with available data the integrated shear strength of the lithosphere decreases with time as the belt is being built and then eroded this evolution is sensitive to belt width if extension occurs when the integrated shear strength drops below a critical value our results yield a framework for comparing different orogenic belts we predict that extension starts late in the history of wide belts and never occurs in narrow belts a final implication of this study is that the average rate of crustal heat production is probably close to 1 1 10 6 w m 3 which is in the upper range of possible values we present a simple and convenient diagram summarizing the thermal characteristics of orogenic belts as a function of width and shortening rate

structural development of the lower paleozoic belt of south china genesis of an intracontinental orogen abstract an extensive structural study of wuyishan and surrounding areas south china brings data on the structures formed prior to the devonian unconformity building the lower paleozoic belt an ordovician tectonic event was responsible for i south directed structures in the wuyishan proper and its southern border related to both thin and thick skinned tectonics accompanied by metamorphism and crustal thickening ii north directed structures to the west of ganjiang fault and north of jiangshan shaoxing fault where only thin skinned tectonics is visible the southward deformation accommodating the shortening includes emplacement of thrust sheets involving deep crustal material and some mantle peridotite and likely repetition of continental material both responsible for crustal thickening the orogeny was due to the underthrusting of the southern part of the south china block beneath the northern part of this block closing the pre existing nanhua rift created at around 850 800 ma and involving the rift sedimentary fill in the southward thrusting the syn metamorphic tectonic piling was followed by anatexis and granite emplacement at around 440 390 ma our new u th pb epma monazite dating gives ages of 433 9 ma and 437 5 ma early silurian for the main anatectic event and a younger age of 412 5 ma late silurian early devonian for a late re heating process the lower paleozoic belt is an intracontinental orogen without oceanic suture record it shows some similarities with the cenozoic european pyrenees chain with a strong asymmetry

mesozoic large scale magmatism and mineralization in south china preface abstract south china is famous for its polymetallic deposits with more than 50 of the world s w and sb reserves and 20 of the sn reserves as well as abundant cu mo pb zn au ag ta nb hree and u this special issue reports recent progress on the tectonic evolution magmatism and ore deposits of south china which leads to a more comprehensive understanding of the mesozoic large scale magmatism and mineralization events 1 south china has been located in backarc settings during multiple subductions since the paleozoic which may have contributed to pre enrichments of the ore forming materials 2 the pacific plate subduction was a principle factor that controlled the late mesozoic large scale magmatism and mineralization in south china through flat subduction ridge subduction slab tearing and slab rollbacks

intracontinental subduction a possible mechanism for the early palaeozoic orogen of se china the early palaeozoic orogen of se china consists of three lithotectonic elements from top to bottom a sedimentary upper unit a metamorphic lower unit and a gneissic basement the boundaries between these units are flat lying south directed ductile decollements the lower one is coeval with an amphibolite facies metamorphism m1 the belt is reworked by migmatite granite domes high temperature metamorphism m2 and granitic plutons related to post orogenic crustal melting we date here the syn m1 ductile shearing at 453 7 ma by u th pb method on monazite previous ages and our new 40 ar 39 ar ages of biotites and muscovites show that the metamorphic rocks experienced syn m2 exhumation from 440 to 400 ma the early palaeozoic orogen of se china is an intracontinental belt in which decollements accommodated the north directed subduction of the cathaysian continent this orogen is an example of intracontinental subduction that was not preceded by oceanic subduction

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

origin of the high temperature olserum djupedal ree phosphate mineralisation se sweden a unique contact metamorphic hydrothermal system abstract the swedish part of the fennoscandian shield hosts a variety of rare earth element ree deposits including magmatic to magmatic hydrothermal types this paper focuses on the origin of the olserum djupedal ree phosphate mineralisation located in the sparsely studied vastervik region se sweden here mineralisation occurs in three main areas olserum djupedal and bersummen primary hydrothermal ree mineralisation formed at high temperatures about 600 c leading to precipitation of monazite ce xenotime y fluorapatite and minor y ree u fe nb ta oxides in veins and vein zones dominated by biotite amphibole magnetite and quartz the veins are hosted primarily by metasedimentary rocks present close to or within the contact aureole of a local 1 8 ga ferroan alkali feldspar granite pluton but also occur within in the chemically most primitive granite in the outermost part of that pluton in the djupedal area ree mineralised metasedimentary bodies are extensively migmatised with migmatisation post dating the main stage of mineralisation in the olserum and bersummen areas the ree bearing veins are cross cut by abundant pegmatitic to granitic dykes the field relationships demonstrate a protracted magmatic evolution of the granitic pluton and a clear spatial and temporal relationship of the ree mineralisation to the granite the major and trace element chemistry of ore associated biotite and magnetite support genetic links between all mineralised areas biotite mineral chemistry data further demonstrate a distinct chemical trend from metasediment hosted ore associated biotite distal to the major contact of the granite to the biotite in the granite hosted veins this trend is characterised by a systematic decrease in mg and na and a coupled increase in fe and ti with proximity to the granite hosted veins the halogen compositions of ore associated biotite indicate elevated contents of hcl and hf in the primary ree mineralising fluid calculated log fhf fhcl values in the olserum area suggest a constant ratio of about 1 at temperatures of 650 550 c during the evolution of the primary hydrothermal system in the djupedal and bersummen areas the fluid locally equilibrated at lower log fhf fhcl values down to 2 high na contents in ore associated biotite and amphibole and the abundance of primary ore associated biotite indicate a k and na rich character of the primary ree mineralising fluid and suggest initial high temperature k na metasomatism with subsequent cooling of the system the fluid evolved locally to more ca rich compositions as indicated by the presence of the ca rich minerals allanite ce and uvitic tourmaline and by the significant calcic alteration of monazite ce the later ca rich stages were probably coeval with low to medium high temperature 200 500 c na ca metasomatism variably affecting the granite and the wall rocks producing distinct white quartz plagioclase rocks all observations and data lead us to discard the prevailing model that the ree mineralisation in the olserum djupedal district represents assimilated and remobilised former heavy mineral rich beds instead we propose that the primary ree mineralisation formed by granite derived fluids enriched in ree and p that were expelled early during the evolution of a local granitic pluton the ree mineralisation developed primarily in the contact aureole of this granite and represents the product of a high temperature contact metamorphic hydrothermal mineralising system the ree mineralisation probably formed synchronously with k na and subsequent na ca metasomatism affecting the granite and the wall rocks the later na ca metasomatic stage is probably related to a regional na ca metasomatic and associated u ree mineralising system operating concurrently with granitic magmatism at c 1 8 ga in the vastervik region this highlights the potential for discovering hitherto unknown ree deposits and for the reappraisal of already known deposits in this part of the fennoscandian shield

crustal structure and contact relationship revealed from deep seismic sounding data in south china abstract a 400 km long wide angle seismic profile in the south china crosses three tectonic domains southeast continental margin of yangtze block northwest continental margin of cathaysia block and south china suture zone separating these two blocks the crustal velocity model constructed from traveltime fitting shows that the crust thickness thins from the northwest to the southeast along the profile it also reveals the crustal contact relationship between the yangtze and cathaysia blocks where the wuchuan sihui fault is the boundary between them combining this profile with two more profiles in the continental south china and three profiles in the northern margin of south china sea constructs a continent ocean transition section this cross section reveals that the moho depth shallows gradually along the cross section from the yangtze block to the cathaysia block and the northern margin of south china sea but shallows abruptly in the continent ocean transition to the south china sea

u pb and hf isotopic study of zircons from migmatised amphibolites in the cathaysia block implications for the early paleozoic peak tectonothermal event in southeastern china abstract amphibolites occur in a number of localities in the cathaysia block some of them have been migmatised and their protoliths represent basaltic magmas erupted in various tectonic settings four migmatised amphibolites were collected from jiangxi and fujian provinces cathodo luminescence images of zircons extracted from the representative amphibolites show unzoned or sector zoned structure la icp ms analysis indicates that most zircons have high th u ratios and yield u pb zircon ages of 446 5 435 2 434 4 and 423 2 ma respectively lu hf isotopic analysis on these zircons gives hf model ages ranging from 900 to 1200 ma based on lithological observations and previously published geochronological data we interpret that these u pb ages record an important tectonothermal event that led to the migmatization this early paleozoic caledonian tectonothermal event in the southeastern china has a great tectonic implication for the evolutionary history of the cathaysia block

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

petrology of basement dominated terranes ii contrasting isotopic sr nd pb and o signatures of basement derived granites and constraints on the source region of granite damara orogen namibia abstract major and trace element and nd sr o and pb isotope data from granites of the high grade central part of the damara orogen khan and outlet gorge areas namibia indicate a dominantly lower crustal origin based on their appearance in field the granites can be divided into red granites white granites and grey granodiorites red granites and some of the white granites from the khan area are isotopically evolved initial e nd 12 5 to 18 9 and were likely derived from metaigneous sources with late archaean to early proterozoic crustal residence ages other white granites are less evolved initial e nd 6 5 to 8 8 and were likely derived from metasedimentary sources that are similar to the country rock metapelites grey granodiorites from the khan and outlet gorge area are also isotopically evolved initial e nd 9 9 to 13 1 but are derived from metaigneous sources with younger late proterozoic crustal residence ages major and trace element data do not support closed system fractional crystallization processes for all samples however some chemical features i e decreasing rare earth element ree abundances with increasing sio 2 underline the importance of crystal fractionation processes for each distinct magmatic pulse isotope data do not support mixing of different crust derived melts or assimilation of crustal rocks by a mafic magma instead highly evolved pb isotope compositions strongly negative e nd values and radiogenic sr isotope compositions argue for an undepleted basement as a potential source the most likely model involves mainly partial melting of different basement rocks of archaean to proterozoic age at different levels within the crust only some granites could be derived by melting of metasedimentary rocks of the pan african cover sequence the consistency of the chemical data with a crustal anatectic origin and the range in radiometric ages suggests that they intruded simultaneously with crustal thickening however some of them may have been emplaced during extensional tectonics c 40 50 ma later than the main period of crustal thickening the heating events that promoted melting of fertile deep crustal rocks might have been caused either by the inferred high heat productivity together with crustal thickening during the main periods of orogeny or by delamination of mantle lithosphere during the final extensional stages of the pan african orogeny

middle to late jurassic felsic and mafic magmatism in southern hunan province southeast china implications for a continental arc to rifting abstract extensive middle to late jurassic felsic and mafic magmatism occurred in the southern hunan province southeast china shrimp zircon u pb dating mineral chemical element geochemical and sr nd hf isotopic data have been determined for these rocks the results indicate that the middle jurassic 178 170 ma changchengling and ningyuan basaltic rocks belong to tholeiitic series and alkaline series respectively and were formed by fractional crystallization of the parent magmas that were derived from partial melting of asthenospheric mantle triggered by the slab released fluids of the subducted paleo pacific plate the late jurassic 152 146 ma daoxian basalts and guiyang lamprophyre dikes are low ti high mg potassic rocks they were derived directly by partial melting of shallower 60 100 km lithospheric mantle composed of amphibole and phlogopite bearing lherzolite in response to thermal perturbations associated with the rifting of continental arc the middle jurassic 164 ma tongshanling granitic rocks belong to calc alkaline series and are strongly peraluminous they were formed by partial melting of palaeoproterozoic metasedimentary basement in the lower crust plus additional input from coeval basaltic magma the late jurassic 156 ma jinjiling and xishan granitic rocks show a2 subtype affinity they were generated by partial melting of granulitized palaeoproterozoic metamorphic basement in the lower crust in response to injection of coeval low ti high mg potassic magmas a moderate degree 56 58 of fractionation of these pure crustal melts could account for more felsic end member of granitic rocks detailed petrologic and geochemical data for the middle to late jurassic felsic and mafic rocks from the southern hunan imply that during the middle jurassic time se china on the southeast of the shi hang zone was a continental arc coupled with the subduction of the palaeo pacific plate and since the beginning of late jurassic time an intra arc rift has been formed along the shi hang zone as a consequence of slab roll back

geochronological and geochemical constraints on the petrogenesis of middle paleozoic kwangsian massive granites in the eastern south china block abstract to achieve a better understanding of the kwangsian orogenic event of the eastern south china block this paper documents a set of new zircon u pb geochronological and hf isotopic data and whole rock elemental and sr nd isotopic analytical results for the representative massive granite intrusions across the jiangshan shaoxing fault the studied samples are classified into two groups representing the rocks from the cathaysia block to the east of the jiangshan shaoxing fault group 1 and those from the eastern yangtze block between the anhua luocheng and jiangshan shaoxing faults group 2 the group 1 samples gave the zircon u pb ages of 405 454 ma and e hf t values of 3 6 to 15 2 with hf model ages of 1 6 2 4 ga group 2 yielded the zircon u pb ages of 400 432 ma and e hf t values of 0 2 to 12 7 with hf model ages of 1 3 2 2 ga geochemically the group 1 samples a cnk 1 02 1 43 have relatively lower al 2 o 3 mgo cao p 2 o 5 and e nd t but higher k 2 o na 2 o than those of group 2 a cnk 0 93 1 44 both groups show similar chondrite normalized patterns of rare earth elements with eu eu values of 0 15 0 92 and strongly negative ba sr nb p and ti anomalies in primitive mantle normalized spider diagrams their e nd t values range from 11 1 to 8 0 for group 1 and 8 9 to 5 0 for group 2 generally similar to those of precambrian paragneiss and contemporaneous gneissoid granites in the eastern south china block our geochronological results indicate that the kwangsian massive granites in the eastern south china block were crystallized between 400 ma and 454 ma synchronous to the kwangsian gneissoid granites along the wugong and wuyi baiyun yunkai domains in the eastern south china block the synthesis of these whole rock geochemical and in situ zircon hf isotopic data suggests that both the group 1 and 2 granites across the jiangshan shaoxing fault were predominantly derived from a crustal source with some proportional metapelitic and metaigneous components from the precambrian basement the input of juvenile mantle derived magma is insignificant taking into account other available evidences it is proposed that the jiangshan shaoxing fault might be a pre existing boundary between the yangtze and cathaysia blocks which was reactivated during the middle paleozoic kwangsian orogenic event the massive granitic magmatism was probably resulted from the doubly crustal thickening and subsequent isostatic readjustment in an intracontinental tectonic regime

a comprehensive upb smnd rbsr and 40ar39ar geochronological study on guidong granodiorite southeast china records of multiple tectonothermal events in a single pluton a complicated tectonothermal history of the guidong granodiorite from the huanan fold belt has been revealed by using combined dating techniques u pb single zircon and whole rock nd model ages suggest that the granodiorite was derived from an ancient crustal source which was probably composed of a mixture of 1 2 2 4 ga crustal materials with a nd model age of 1 6 ga the granodiorite emplacement age of 427 3 ma is defined by concordant u pb single zircon analysis plagioclase biotite hornblende apatite sphene and whole rock yield an internal sm nd isochron age of 428 12 ma consistent within the analytical errors with the u pb zircon age due to the presence of inherited zircon however the zircon data point deviates from the sm nd isochron four whole rocks and two mineral separates plagioclase and hornblende yield a rb sr isochron age of 422 14 ma which is coincident with zircon u pb and sm nd isochron ages hornblende 40ar 39ar step heating analysis gives a main plateau age of 371 4 1 3 ma which is considerably younger than the crystallization age this age is interpreted as recording a post crystallization folding event which produced the prominent unconformity between pre devonian and middle devonian strata and resulted in the deformation of all major minerals of the granodiorite since most deformed minerals have remained closed to sm nd and rb sr isotopic migration since emplacement of the granodiorite it can be suggested that this folding event took place without significant fluid circulation and contemporaneous metamorphism a low temperature heating step of hornblende yields an apparent 40ar 39ar age of 208 5 2 0 ma which may or may not have a connection to the minimum age of the huanan indosinian orogeny a biotite 40ar 39ar age spectrum yields much younger apparent ages of 145 and 92 ma which are coincident with two important yanshanian magmatic episodes

detrital zircon u pb geochronology hf isotopes and geochemistry constraints on crustal growth and mesozoic tectonics of southeastern china abstract in situ u pb geochronological hf isotopic and ree geochemical analyses of detrital zircons from mesozoic sandstones in central jiangxi and east hunan of the south china block scb are used to provide not only information about crustal evolution process but more importantly new constraints on sedimentary provenances as well as mesozoic basin evolutions in central scb a total of 417 concordant zircon analyses define five u pb age populations at ca 2 6 2 3 ga ca 2 0 1 7 ga ca 1 0 0 7 ga ca 500 400 ma and ca 300 200 ma integrated analyses of zircon u pb ages and hf isotopes of detrital zircons reveal five episodes of juvenile continental crust growth ca 2 5 ga ca 1 7 ga ca 850 ma ca 440 ma and ca 230 ma with all but the ca 2 5 ga episode likely represent that of the scb none of the three samples from t3 j1 strata showed strong ca 1850 ma and ca 230 ma peaks suggesting that the t3 j1 sediments probably sourced from the yangtze block in contrast stronger peaks of ca 1850 ma and ca 250 230 ma in post j1 strata relative to that of t3 j1 strata suggest a dominantly local cathaysian provenance in addition the distinct low ehf t values for zircons of ca 430 ma from t3 j1 strata in comparison with higher ehf t values for that from post j1 strata also support aforementioned viewpoint such sharp changes between the pre j1 and post j1 strata coincide with the remarkable change in regional palaeogeography from a broad shallow marine basin in the late triassic early jurassic time to a basin and range style province in the middle jurassic the characteristics and time evolution of detrital zircons from the studied area are consistent with the flat slab subduction model which involves the development of a broad sag basin during the t3 j1 time and a rapid regional uplift in the cathaysia block caused by the reinitiating of normal subduction along the coastal region at ca 190 ma

crustal origin of hercynian peraluminous granitic batholiths of central spain petrological geochemical and isotopic sr nd constraints abstract in central spain it is possible to distinguish two main types of peraluminous late hercynian granites the pi types and the ps types the distinction between both types is made on the basis of differences in peraluminosity ps types are more peraluminous than pi types and also on the appearance of some characteristic mafic minerals ps types have biotite cordierite and monazite as the most typical accessory phase whereas pi types have biotite amphibole in the less evolved facies and allanite as the accessory mineral both granite types have similar trace element ratios and initial sr nd and pb isotopic signatures initial 87sr 86sr ratios of both types exhibit a large range from 0 7073 to 0 7193 whereas initial end varies in a restricted range from 5 4 to 6 6 the scarce associated basic rocks do not play a significant role in the chemical variability of these peraluminous granites which follow low pressure crystal fractionation trends from granodiorite monzogranite parental magmas mixing and afc modelling of sr and nd isotopic data reveal an unrealistically high mantle contribution based on major and trace element and isotopic data an orthogneissic protolith for both granitic series is proposed nevertheless none of the metamorphic country rocks of central spain has the appropriate sr isotopic composition to satisfy the origin of these granitic rocks and so it is argued that progressive isotopic re equilibration of crustal material during the granulization of the lower hercynian crust together with the possibility of isotopic disequilibrium during melting as has been demonstrated in migmatitic terranes in nearby areas may explain the isotopic differences between the granites and the high level metamorphic country rocks

contrasting geochemical and sm nd isotopic compositions of archean metasediments from the kongling high grade terrain of the yangtze craton evidence for cratonic evolution and redistribution of ree during crustal anatexis abstract twenty three clastic metasediments from the kongling high grade terrain of the yangtze craton south china were analyzed for major trace and rare earth elements and sm nd isotopic ratios associated dioritic tonalitic trondhjemitic dtt and granitic gneisses as well as amphibolites were also analyzed in order to constrain provenance the results show that the clastic metasediments can be classified into 3 distinct groups in terms of mineralogical geochemical and sm nd isotopic compositions group a is characterized by having no to slight negative eu anomalies eu eu 0 82 1 07 being high in cr 191 396 ppm and ni 68 137 ppm and low in th 3 3 7 8 ppm and ree ree 99 156 ppm these characteristics are similar to those of metasediments from archean greenstone belts in addition the group a metasediments have the value of the chemical index of alteration ciw close to felsic gneisses their sm nd isotopic ree and trace element compositions can be interpreted by mixtures of the dtt gneisses and amphibolites dating of detrital zircons from 2 group a samples by shrimp reveals a major concordant age group of 2 87 3 0 ga which is identical to the age of the trondhjemitic gneiss these results strongly suggest that group a was principally the first cycle erosion product of the local kongling dtt gneiss and amphibolite moreover the higher than amphibolite cr content and slight eu depletion exhibited by some samples from this group infer that ultramafic rocks like komatiite and granite of probably 3 0 3 3 ga in age also played a role group b is characterized by the presence of graphite and shows a more evolved composition similar to post archean shales with a prominent negative eu anomaly eu eu 0 48 0 77 and high ciw on paired cr th vs la co and co th plots group b samples conform to a two end member mixing line of the kongling granitic gneiss and amphibolite however data on nd model age and ciw suggest that the granite component should be younger than the sampled granitic gneiss and derived from a distal source both groups a and b exhibit a clear positive correlation between ciw and tdm and a negative one between ciw and eu eu these correlations point to the crustal evolution of the yangtze craton towards coupled increasing ciw and eu depletion with decreasing age this in turn reflects the change of granitoid magmatism from local na rich dioritic tonalitic trondhjemitic rocks to widespread k feldspar granite the change led to the intracrustal differentiation stabilization and growth of the craton group c is restite and contains abundant sillimanite and garnet and unusually high ilmenite 7 11vol which can be seen to be dehydration melting products of biotite under the microscope this group shows extremely varied ree distributions from lree enriched to depleted and from negative to strong positive eu eu 1 63 eu anomalies compared to groups a and b group c is severely depleted in na2o k2o lree rb and ba whereas tio2 co v sc and hree and y are considerably enriched this is accompanied by anomalous high sm nd 0 21 0 28 147sm 144nd 0 1361 0 1738 and 143nd 144nd 0 511589 0 511958 ratios tdm correlates clearly with sm nd ratio and 2 out of 3 samples give significantly older to unrealistic tdm 3 9 4 9 ga the results document redistribution of ree and an open behavior of the sm nd isotope system during the biotite dehydration melting of metasediments

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

anatexis and metamorphism in tectonically thickened continental crust exemplified by the sevier hinterland western north america the generation of granitoid magmas by partial melting of crustal rocks during continental thickening events is well documented in many geological provinces throughout the world including the late mesozoic sevier belt of western north america we present a thermal and petrologic model of anatexis and metamorphism in regions of crustal thickening where the only mantle contribution is the normal conductive supply of heat through the base of the lithosphere i e advection of mass and energy are excluded we distinguish between formation of migmatites and generation of mobile granitoid magmas and examine the temporal and spatial relationships between these two distinct anatectic processes between anatexis and regional deformation and between anatexis and metamorphism a fundamental conclusion is that if protoliths rich in hydrous minerals are present regional anatexis is the end product of classical barrovian metamorphism in thickened continental crust even in the absence of a free water rich fluid phase barrovian metamorphic facies series are predicted with thickening ratios maximum crustal thickness attained initial crustal thickness as low as 1 3 but mobile granitoid magmas are not formed if this ratio is less than approximately 1 5 above these lower bounds barrovian metamorphism and anatectic granitoid magmatism occur independently of the magnitude of thickening and of the way in which thickening is accomplished both processes are sensitive to a diminished heat supply lowering either moho heat flow or crustal radioactive heat production results in blueschist eclogite metamorphism and inhibits the formation of mobile granitoid magmas we model anatexis under fluid absent conditions and show that with such a constraint migmatization is always a syn kinematic process relative to the crustal thickening event whereas generation of mobile granitoid magmas is in most cases post kinematic relative to crustal thickening but can be syn kinematic if thickening takes more than approximately 50 myr the typical time intervals for melting are consistent with geological observations mobile granitoid magmas are predicted by most of our models within approximately 10 myr of the end of the crustal thickening event this incubation period results primarily from the temperature increase required for the dehydration melting reactions capable of producing large melt fractions to occur the energetic requirements of anatexis are relatively minor compared to conductive crustal thermal budgets as shown by the fact that once the necessary p t conditions are attained melting reactions are completed within time intervals on the order of 1 myr i e 1 2 orders of magnitude smaller than the characteristic time scales of the tectonic processes involved in crustal thickening

triassic high strain shear zones in hainan island south china and their implications on the amalgamation of the indochina and south china blocks kinematic and 40ar 39ar geochronological constraints abstract a kinematic and geochronological study has been carried out on the triassic high strain shear zones in hainan island the southern south china block there are wnw and ne trending high strain shear zones with greenschist to amphibolite facies metamorphism in this island kinematic indicators suggest a dextral top to the nne thrust shearing for the wnw trending high strain shear zones and a sinistral top to the se thrust shearing for the ne trending shear zones the quartz c axis orientations of mylonitic rocks exhibit the domination of basal slip and some activation of a rhombohedra gliding system the timing of shearing for these shear zones has been constrained by the 40ar 39ar dating analyses of synkinematic minerals middle triassic 242 250 ma and late triassic early jurassic 190 230 ma have been identified for the wnw and ne trending shear zones respectively a synthesis of these kinematic and thermogeochronological data points to a two stage tectonic model for hainan island that is top to the nne oblique thrusting at 240 250 ma followed by top to the se oblique thrusting at 190 230 ma in combination with the available data from the southern south china and indochina blocks it is inferred that south hainan and north hainan have affinity to the indochina and south china blocks respectively the tectonic boundary between south hainan and north hainan lies roughly along the wnw trending changjiang qionghai tectonic zone probably linking to the song ma and ailaoshan zones the middle triassic structural pattern of hainan island is spatially and temporally compatible with those of the south china and indochina blocks and thus might be a derivation from the amalgamation of the indochina with south china blocks in response to the closure of the paleotethys ocean and subsequent subduction collision

structural signatures and 40ar 39ar geochronology of the indosinian xuefengshan tectonic belt south china block abstract to advance our understanding of the kinematics of the xuefengshan tectonic belt xfstb and the mesozoic tectonics of the south china block scb this paper presents new data and interpretations from our structural studies and thermochronological dating the xfstb is characterized by greenschist facies metamorphism and development of s and s l tectonic fabrics an asymmetric positive flower structural pattern is composed of nw wnw and se ese dipping cleavages faults and shear zones kinematic indicators indicate a dominant top to wnw thrusting with a sinistral strike slip component on the ese dipping shear zones and top to ese back thrusting on the wnw dipping shear zones the quartz c axis orientations of mylonitic rocks exhibit monoclinic point maximum asymmetry indicative of a sinistral shear sense under the a basal gliding condition the timing of the major deformation event has been constrained to the middle triassic to early jurassic 244 195 ma on the basis of 40ar 39ar geochronology and other geological observations the structural characteristics of the xfstb are probably related to an indosinian oblique convergent zone in combination with tectonic wedging and associated back thrusting all above a low angle se dipping basal detachment oblique northwestward and upward movement along the basal detachment was partitioned into the nw wnw directed thrusting se ese directed back thrusting and subsidiary strike slip movement along the ne and nne trending faults and shear zones the xfstb may represent part of a huge structural fan between the yangtze and cathaysian blocks and can be interpreted as a product of the indosinian intracontinental collision involving a weak zone

kwangsian crustal anatexis within the eastern south china block geochemical zircon u pb geochronological and hf isotopic fingerprints from the gneissoid granites of wugong and wuyi yunkai domains abstract gneissoid granites were traditionally thought to be the components of the precambrian basement in the eastern south china block but twenty four gneissoid granite samples from the wugong northern wuyi southern wuyi and yunkai domains gave zircon u pb ages of 424 456 ma 410 457 ma 426 438 ma and 415 450 ma respectively the existence of the abundant kwangsian gneissoid granites which have incorrectly been assigned to the precambrian basement indicates that the so called precambrian stratigraphic sequence of the cathaysia block should be termed complex rather than group these gneissoid granites are peraluminous granites with relatively high al 2 o 3 mgo tio 2 feot and cao na 2 o but low cao al 2 o 3 mgo feot and rb sr ratios they exhibit strongly negative ba sr nb p and ti and positive pb anomalies in primitive mantle normalized diagrams and have initial 87 sr 86 sr ratios ranging from 0 70924 to 0 72935 and negative end t values from 6 4 to 11 4 similar to those of paragneissic enclaves and precambrian sedimentary rocks in the eastern south china block the zircons crystallized in the kwangsian gneissoid granites gave ehf t values ranging from 2 4 to 19 4 with the peak at 4 almost all grains clustering at 1 to 12 and hf model ages of 1 1 2 1 ga the synthesis of these geochemical and in situ zircon hf isotopic data indicates that the kwangsian gneissoid granites dominantly originated from proterozoic metapelitic and meta igneous components with insignificant input of juvenile mantle derived magmas a model of two stage crustal anatexis is proposed for the kwangsian granitic magma in the eastern south china block with 1 the formation of 460 430 ma granite through the breakdown of hydrous minerals under the condition of the doubly thickened crust and 2 the generation of the 430 400 ma granite accompanying promoted melting along a path of isothermal decompression due to the increasing thermal weakening for the collapse of the thickened crust the crustal anatexis has probably occurred in an intracontinental tectonic regime that was geodynamically linked to the far field response to the assembly of the australian indian plate with the cathaysia block during middle paleozoic kwangsian time

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

components and episodic growth of precambrian crust in the cathaysia block south china evidence from u pb ages and hf isotopes of zircons in neoproterozoic sediments abstract detailed lam icpms u pb dating and lam mc icpms lu hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern cathaysia block south china the chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary zircon u pb dating results show they mainly formed during the late neoproterozoic the precambrian crust of the cathaysia block can be divided into two distinct tectonic domains the wuyishan terrane to the northeast and the nanling yunkai terrane to the southwest the nearly e w boundary between these two terranes is also supported by geophysical petrological and geochemical evidence and the basement rocks of the two terranes are comprised of different components the wuyishan terrane is characterized by dominant paleoproterozoic 1 86 ga and lesser neoarchean magmatism and the southern central part of the terrane suffered strong neoproterozoic and early paleozoic tectonothermal reworking the zircon data suggest that there were five important episodes of juvenile crust generation 3 6 ga 2 8 ga 2 6 2 4 ga 1 85 ga and 0 8 0 7 ga in the wuyishan terrane strong paleoproterozoic 1 85 ga magmatism in northern wuyishan and neoproterozoic 0 8 0 7 ga magmatism in central and southern wuyishan both principally involved the remelting of old crust with minor input of juvenile material in contrast the nanling yunkai terrane contains abundant neoarchean and grenvillian zircons some evidence of mesoproterozoic activity and rare paleo to meso archean and neoproterozoic zircons u pb ages and hf isotopic compositions of the detrital zircons from the late neoproterozoic to early paleozoic meta sedimentary rocks in the nanling yunkai area suggest that the growth of juvenile crust mainly occurred at 3 6 ga 3 3 ga 2 5 2 6 ga 1 6 ga 1 0 ga and 0 8 0 7 ga neoarchaean 2 6 2 5 ga grenvillian 1 0 ga and neoproterozoic 0 8 0 7 ga magmatism mainly involved the recycling of old crust minor remnants of 4 1 ga crust may remain in the terrane this crustal history is distinct from that of the wuyishan terrane and analogous to those recorded for the eastern india east antarctic domain of northern gondwanaland suggesting that they probably were once linked

zircon u pb age hf isotopic compositions and geochemistry of the silurian fengdingshan i type granite pluton and taoyuan mafic felsic complex at the southeastern margin of the yangtze block abstract this work presents an integrated study of zircon u pb ages and hf isotope along with whole rock geochemistry on silurian fengdingshan i type granites and taoyuan mafic felsic intrusive complex located at the southeastern margin of the yangtze block filling in a gap in understanding of paleozoic i type granites and mafic intermediate igneous rocks in the eastern south china craton scc the fengdingshan granite and taoyuan hornblende gabbro are dated at 436 5 ma and 409 2 ma respectively the fengdingshan granites display characteristics of calc alkaline i type granite with high initial 87sr 86sr ratios of 0 7093 0 7127 low end t values ranging from 5 6 to 5 4 and corresponding nd model ages t2dm of 1 6 ga their zircon grains have ehf t values ranging from 2 7 to 2 6 and model ages of 951 1164 ma the taoyuan mafic rocks exhibit typical arc like geochemistry with enrichment in rb th u and pb and depletion in nb ta they have initial 87sr 86sr ratios of 0 7053 0 7058 end t values of 0 2 1 6 and corresponding t2dm of 1 0 1 1 ga their zircon grains have ehf t values ranging from 3 2 to 6 1 and model ages of 774 911 ma diorite and granodiorite from the taoyuan complex have initial 87sr 86sr ratios of 0 7065 0 7117 end t values from 5 7 to 1 9 and nd model ages of 1 3 1 6 ga the petrographic and geochemical characteristics indicate that the fengdingshan granites probably formed by reworking of neoproterozoic basalts with very little of juvenile mantle derived magma the taoyuan complex formed by magma mixing and mingling in which the mafic member originated from a metasomatized lithospheric mantle both the fengdingshan and taoyuan plutons formed in a post orogenic collapse stage in an intracontinental tectonic regime besides the paleozoic fengdingshan granites and taoyuan hornblende gabbro other neoproterozoic and indosinian igneous rocks located along the southeastern and western margin of the yangtze block also exhibit decoupled nd hf isotopic systemics which may be a fingerprint of a previous late mesoproterozoic to early neoproterozoic oceanic subduction

a possible linkage between highly fractionated granitoids and associated w mineralization in the mesozoic yaogangxian granitic intrusion nanling region south china abstract the yaogangxian ygx w deposit in the central nanling w province south china is one of the largest w deposits worldwide both vein type wolframite and skarn type scheelite orebodies were exposed in ygx these scheelite and wolframite mineralization are spatially associated with the ygx granitic intrusion the exposed intrusion contains two main intrusive phases lower zone coarse grained two mica granite and upper zone fine grained muscovite granite an integrated study of whole rock geochemistry la icp ms zircon u pb geochronology and zircon hf isotopic geochemistry of the ygx granitic intrusion was undertaken to constrain its magmatic source and petrogenesis cassiterite la icp ms u pb dating was also undertaken to constrain the connection between the intrusion and hydrothermal w mineralization zircon u pb dating yielded weighted mean ages of 161 3 and 157 2 ma for the two mica and muscovite granites respectively cassiterite crystals from wolframite quartz veins display growth zonation under cathodoluminescence and have a weighted mean zircon u pb age of 158 2 ma the formation of the muscovite granite and related w mineralization in the ygx deposit was thus initiated during the early yanshanian the ygx granites display typical metaluminous to strongly peraluminous characteristics with high sio2 73 5 79 1 wt and k2o 3 0 5 0 wt contents they are enriched in heavy rare earth elements rees comparative to light rees notably they exhibited strong negative eu anomalies and are depleted in sr ba p and ti in addition muscovite granites in ygx are more significantly enriched in heavy rees relative to light rees than two mica granites indicating that the former experienced higher degree fractionation than the latter zircon grains of the ygx granitoids have strongly negative ehf t 15 to 10 3 with two stage hf model ages of 2 15 1 86 ga indicating a magma source of reworked ancient crustal material without obvious involvement of juvenile materials the results of petrology and geochemistry indicate that the ygx granitic intrusion is a highly fractionated s type granite emplaced during widespread 160 150 ma granitic magmatism in the nanling region further evolution to late stage for multiphase ygx granitic intrusion is needed to enrich ore forming elements after magmatic emplacement it is suggested that the extensional environment of continental lithosphere caused by the northwest subduction of the paleo pacific plate may play an key role in the genesis of ygx s type granite w rich proterozoic basement rocks and fractional crystallization may provide material for the formation of the granite related tungsten mineralization

late ordovician to earliest silurian graptolite and brachiopod biozonation from the yangtze region south china with a global correlation late ordovician to earliest silurian is an important geological period marked by large geological and biological events however the strata and fossils of this interval are not complete in many parts of the world based on studies of 43 sites in south china in particular the continuous sections on the yangtze platform we recognize a complete succession including seven graptolite zones and two shelly faunas in ascending order the graptolite zones are the dicellograptus complanatus dicellograptus complexus paraorthograptus pacificus including lower subzone tangyagraptus typicus subzone and diceratograptus mirus subzone normalograptus extraordinarius normalograptus ojsuensis normalograptus persculptus akidograptus ascensus and parakidograptus acuminatus zones the shelly faunas are the foliomena nankinolithus and hirnantia faunas which may be correlated with d complanatus zone and n extraordinarius n ojsuensis to part of n persculptus zones respectively the biozonation through this interval from the yangtze region can be correlated with that of other parts of the world such as dob s linn in scotland spain and portugal thuringia saxonia bavaria bohemia poland kazakhstan kolyma malaya peninsula yukon canadian arctic islands nevada argentina niger and victoria australia the hirnantian substage which has been proposed by us recently includes the n extraordinarius n ojsuensis zone hirnantia fauna and n persculptus zone the base of the hirnantian substage is marked by the first appearance data fads of n extraordinarius and n ojsuensis which have been determined to be synchronous on a global scale

the western segment of the suture between the yangtze and cathaysia blocks constraints from inherited and co magmatic zircons from permian s type granitoids in guangxi south china the location of the suture between the yangtze craton and the cathaysia block is uncertain in the west three proposed locations for the western segment of the suture all go through guangxi but are up to 150 km apart inherited zircon crystals from the darongshan permian s type granitoid plutons which are derived from the lower crust and occur north of the southernmost location for the suture yield u pb ages with a major peak at 960 ma the ehf t values of the inherited zircons with ages around the major peak vary from 6 4 to 23 4 the age distribution and hf isotope variations of the inherited zircons are remarkably similar to those of precambrian detrital zircon crystals from the western cathaysia block but strikingly different from those of precambrian detrital zircon crystals from the yangtze craton these results indicate that the western part of the suture is situated to the north of the darongshan granitoid belt

late neoproterozoic early paleozoic evolution of the south china block as a retroarc thrust wedge foreland basin system the early paleozoic wuyi yunkai fold belt of south china represents a major orogenic belt in east asia however its formation is not well understood this paper evaluates the origins of the neoproterozoic early paleozoic basin and the southern margin of the south china block scb based on a compilation of the spatiotemporal evolution of the late neoproterozoic early paleozoic strata and their depositional environments these data are combined with high resolution structural geochronologic metamorphic and petrologic data that are published from the region a new model of a retroarc thrust wedge foreland basin system is proposed for the succession based on the following 1 the nature of the basal unconformity 2 the wedge shaped basin fill geometry bounded by the mountain belt to the south 3 basinward propagation of the thrust front with time and 4 the presence of a typical underfilled stratigraphic trinity of the foreland basin the proposed model suggests two major cycles of evolution of the retroarc thrust wedge foreland basin system 725 635 and ca 564 446 ma which record two periods of northwestward subduction of the oceanic slab beneath the southern margin of the scb terrane accretion is inferred to have taken place during the late stage of these cycles

petrogenesis of the early silurian dashuang high mg basalt andesite dacite in eastern south china origin from a palaeosubduction modified mantle the early paleozoic kwangsian event the first compressive orogeny after the rodinia assemblage in the south china block scb is characterized by the angular unconformity between the devonian and pre devonian sequences and widespread granitoids and small volume mafic rocks however the mechanism triggering this event is highly debated and the associated mantle source is poorly known our recent investigations identified the occurrence of early silurian high mg basalt andesite dacite in the dashuang area along the northwestern yunkai domain in the scb this study presents a set of new zircon u pb geochronological whole rock geochemical and sr nd isotopic data for these volcanic rocks they yield weighted mean 206 pb 238 u ages of c 430 443 ma similar to the age peaks of early middle paleozoic magmatism and metamorphism in the scb these volcanic rocks have high mgo cr and ni contents and mg numbers they also exhibit arc like geochemical affinities with crustal like sr nd isotopic compositions similar to the neoproterozoic high mg basalt andesite in the eastern scb such signatures combined with other geological observations suggest that the dashuang high mg rocks were derived from an ancient probably early neoproterozoic mantle wedge source the early paleozoic intra continental reactivation in response to late orogenic extension triggered the melting of this palaeosubduction modified mantle which led to the formation of these volcanic rocks

the petrogenesis of some migmatites and granites central damara orogen namibia evidence for disequilibrium melting wall rock contamination and crystal fractionation

petrogenesis and tectonic significance of a mesozoic granite syenite gabbro association from inland south china article i nfo a granite syenite gabbro association from inland south china has been studied for zircon u pb ages and hf isotopic compositions as well as whole rock elemental and sr nd isotopic compositions to constrain their sources and tectonic settings these rocks have distinctive crystallization ages the longyuanba biotite granites have a mean age of 240 ma the longyuanba two mica granites pitou alkali feldspar granites and amphibole bearing alkali feldspar granites tabei and huangbu syenites and chebu and chenglong gabbros have a similar age of 178 ma whereas the dafengnao syenite gives a mean age of 165 ma the longyuanba biotite granites and two mica granites exhibit s type characteristics probably derived from a neoproterozoic crustal source the chenglong gabbro has oib like trace element and highly depleted isotope compositions ehf t 10 0 1 3 end t 5 2 suggesting its parental melt to be of asthenospheric origin with insignificant crustal assimilation however crustal contamination is required to explain the isotopic compositions of the chebu gabbro the syenites are shoshonitic in composition and have depleted sr nd hf isotopic signatures which we interpret to have resulted from a mixed source of asthenospheric mantle and metasomatized lithospheric mantle as expected the signals of crustal assimilation are conspicuous in the petrogenesis of the more evolved syenites the pitou alkali feldspar granite and amphibole bearing alkali feldspar granite exhibit i type and a type characteristics respectively they are isotopically more depleted than the s type longyuanba granites we suggest that they may have formed through magma mixing of predominantly mantle derived melts with the neoproterozoic crust the jurassic granite syenite gabbro association was the product of asthenosphere lithosphere crust interactions which records the primary role of asthenospheric mantle upwelling in magma generation both in the mantle and in the crust in the early yanshanian time in south china they probably occurred in an intraplate rift like environment as a tectonic response to far field stress at plate margins during the early stage of the paleo pacific plate subduction the tectonic transition from the tethys orogenic regime to the paleo pacific regime was accomplished in the early jurassic and the early yanshanian magmatism should be genetically associated with the paleo pacific tectonic regime

age and granite association of skarn w mineralization at niutangjie district south china block abstract numerous w sn deposits are developed in the south china block with the majority related to the yanshanian jurassic to cretaceous granites a smaller number of deposits have been found associated with kwangsian middle paleozoic granites the largest of which is the niutangjie skarn w deposit the niutangjie deposit is spatially associated with two suites of granites the unmineralized yuechengling biotite and two mica granites have zircon u pb ages of 427 1 2 9 ma and 427 5 3 5 ma respectively whereas the mineralized niutangjie muscovite granite yields a younger age of 421 0 1 5 ma u pb dating of cassiterite coexisting with scheelite from the niutangjie muscovite granite indicates a mineralization age of 420 8 8 0 ma consistent with the age of the host rock the unmineralized yuechengling biotite granites have a cnk ratios of 0 97 1 16 and show characteristics of both i type and s type granites in contrast the mineralized niutangjie muscovite granites are s type granites with a cnk ratios of 1 12 1 72 and have higher sio2 contents and rb sr ratios and lower nb ta zr hf and k rb ratios than the unmineralized yuechengling biotite granites geochemical differences together with zircon hf isotopic compositions indicate that the relatively fractionated mineralized niutangjie muscovite granites were generated by partial melting of proterozoic meta sediments whereas the unmineralized yuechengling biotite granites were derived from partial melting of proterozoic meta sediments with subordinate meta igneous rocks the unmineralized yuechengling two mica granites have similar geochemical characteristics to the mineralized niutangjie muscovite granites but their relatively small volumes and lack of exploration may explain why the yuechengling two mica granites have not so far been found to be mineralized similarly the larger volume and more highly fractionated nature of the mesozoic yanshanian mineralized granites may explain the greater abundance of w sn mineralization associated with these rocks compared to the paleozoic kwangsian granites

mirror image thrusting in the south china orogenic belt tectonic evidence from western fujian southeastern china abstract the mesozoic orogenic belt in south china is readily divided into two fold and thrust belts and a central multiply deformed zone of ductile deformation dominated by folds with steeply dipping axial planes southeast directed thrusting in the eastern belt and northwest directed thrusting in the western belt resulted in a mirror image of one another during the mesozoic the eastern fold and thrust belt can be further divided into three domains that overlap one another and exhibit a southeast verging wedge like geometry and kinematics deviatoric stress has been calculated from quartz dislocation density at 91 5 mpa 74 5 mpa and 73 8 mpa decreasing toward the southeast upper devonian and lower carboniferous sandstones have been used to constrain bed length for cross section balancing to estimate crustal shortening from three typical areas these indicate 45 41 6 and 37 3 shortening and suggest that 110 km of contraction has been achieved as a result of thrusting this orogen correlates with the ogcheon belt in south korea to the northeast to the southwest it appears to correlate with a thrust belt in western guangdong this southeast verging thrusting may be at least partially controlled by cathaysia to the east

early paleozoic intracontinental granites in the guangzhou region of south china partial melting of a metasediment dominated crustal source abstract whether the formation of early paleozoic granites in the south china block was related to intracontinental orogenic processes or oceanic subduction continues to be debated here we present whole rock major element trace element and sr nd isotopic data as well as secondary ion mass spectrometry and laser ablation inductively coupled plasma mass spectrometry zircon u pb geochronological and hf o isotopic data from biotite two mica and muscovite granites in the baiyunshan and maofengshan areas of guangzhou city south china zircon u pb ages reveal that these rocks were formed during the early paleozoic 446 438 ma these muscovite and biotite bearing granites have high sio2 69 0 80 4 wt and k2o 3 19 5 32 wt contents and low mgo 0 46 1 17 wt contents the granites are enriched in rb th u and pb and depleted in ba sr nb and ti the baiyunshan muscovite granites and maofengshan biotite granites are slightly to moderately enriched in light rare earth elements lrees la yb cn 2 27 15 1 with slight to pronounced negative eu anomalies eu eu 0 27 0 72 whereas the baiyunshan two mica granites are significantly enriched in lrees la yb cn 19 6 32 1 with moderate negative eu anomalies eu eu 0 42 0 58 these muscovite and biotite bearing granites have enriched whole rock nd and zircon hf isotopic compositions end t 12 1 to 7 6 ehf t 11 4 to 0 8 and high zircon 18o values 8 5 10 0 we suggest that the baiyunshan granites were formed by partial melting of metasedimentary rocks as they contain primary muscovite and have high zircon 18o values the maofengshan granites were formed by partial melting of a hybridized crustal source containing metasedimentary rocks with subordinate amphibolites as they have high zircon 18o values variable whole rock sio2 contents and biotite compositions similar to those crystallized in i and s type magmas these granites along with the widespread early paleozoic s type granites in the wuyi yunkai orogen are distributed across a broad area rather than in a narrow belt in addition early paleozoic s type granites in the south china block generally do not show younging trends from east to west or south to north moreover the baiyunshan maofengshan granites show geochemical characteristics similar to syn or post collisional granites and different from volcanic arc granites we therefore propose that these muscovite and biotite bearing granites were formed in an intracontinental orogenic setting

shrimp u pb zircon geochronology and geochemistry of metavolcanic and metasedimentary rocks in northwestern fujian cathaysia block china tectonic implications and the need to redefine lithostratigraphic units abstract northwestern fujian province is one of the most important pre palaeozoic areas in the cathaysia block of south china metavolcano sedimentary and metasedimentary rocks of different types ages and metamorphic grades granulite to upper greenschist facies are present and previously were divided into several formations and groups tectonic contacts occur between some units whereas deformed unconformities have been reported between others new shrimp u pb zircon ages presented here indicate that the original lithostratigraphy and the old group and formation terminology should be abandoned thus the tianjingping formation was not formed in the archaean or palaeoproterozoic as previously considered but must be younger than its youngest detrital zircons 1790 ma but older than regional metamorphism 460 ma besides magmatic zircon ages of 807 ma obtained from metavolcano sedimentary rocks of the nanshan formation and 751 728 ma for the mamianshan group many inherited and detrital zircons with ages ranging from 1 0 to 0 8 ga were also found in them these ages indicate that the geological evolution of the study area may be related to the assembly and subsequent break up of the rodinia supercontinent the new zircon results poorly constrain the age of the mayuan group as neoproterozoic to early palaeozoic 728 458 ma and not palaeoproterozoic as previously thought many older inherited and detrital zircons with ages of 3 6 2 8 2 7 2 6 2 5 2 0 1 8 and 1 6 ga were found in this study a 3 6 ga detrital grain is the oldest one so far identified in northwestern fujian province as well as throughout the cathaysia block nd isotope tdm values of eight volcano sedimentary and clastic sedimentary rock samples centre on 2 73 1 68 ga being much older than the formation ages of their protoliths and thus showing that the recycling of older crust played an important role in their formation these rocks underwent high grade metamorphism in the early palaeozoic 458 425 ma during an important tectono thermal event in the cathaysia block