review of geochemical variation in lower palaeozoic metabasites from the ne bohemian massif intracratonic rifting and plume ridge interaction

strain distribution over the east mediterranean ridge a synthesis incorporating new sea beam data abstract we present the results of several multi narrow beam sea beam traverses of the mediterranean ridge on board r v jean charcot these results can be considered to be complementary in resolution and coverage to the previously published long range side scan sonar gloria results a characteristic of the mediterranean ridge is the presence over about half of its surface of an extensive fold system affecting the messinian and plio quaternary cover which is dissected by conjugate strike slip faults the resolution of sea beam was used to map the main characteristics of folding and faulting this analysis together with previously available data enables us to define the strain pattern over the mediterranean ridge we thus now have an overall view of the strain pattern from a marginal basin aegea through the hellenic trench and adjacent sea floor to the opposite continent the bottom of the hellenic trench is a boundary between an extensional domain to the north and a compressional one to the south the southern domain is strongly affected by the presence of the lybian promontary it is related to the formation of an accretionary ridge due to the inability of the upper 3 4 km of sediments to subduct this ridge is similar to the accretionary prism but it is much wider with respect to its height probably because of the existence of a decollement over a level of overpressure the hellenic trench then is in the situation of a fore arc basin its origin is due to the fact that the aegean continental slope is not vertical but rather has a small 4 dip as a result a sedimentary wedge symmetric but shorter than the main accretionary wedge develops over the buried portion of the slope it is characterized by landward thrusts such an origin probably applies to fore arc basins in general

the eastern continuation of the cadomian orogen u pb zircon evidence from saxo thuringian granitoids in south western poland and the northern czech republic we report u pb single zircon ages from three pre variscan granitoids in the ne part of the bohemian massif the platerowka granodiorite from the lausitz izera unit the polish sudetes has been dated at 533 9 ma the bitouchov granite form the sw part of the south krkonose unit the czech sudetes gave an age of 540 11 10 ma and the w droze granodiorite in the fore sudetic block yielded 548 9 ma all these latest vendian early cambrian granitoids represent the post tectonic expression of a late proterozoic cadomian orogenic cycle and demonstrate the eastward extent of the cadomian basement into the variscan orogen granodiorites of similar age have so far been reported from brittany and especially from the saxo thuringian terrane to the ne and sw of the elbe fault zone we conclude that the saxo thuringian terrane extends across the elbe and sudetic marginal fault zones into the fore sudetic block

the western mediterranean extensional basins and the alpine orogen the western mediterranean late oligocene miocene basins alboran valencia and provencal basins are a coherent system of interrelated troughs in all basins normal faults and thermal subsidence migrated toward the east progressively moving to the miocene to pleistocene algerian and tyrrhenian basins all those troughs appear elements of the back arc opening related to the eastward roll back of the w directed apennines maghrebides subduction zone similarly to western pacific back arc settings these late oligocene early miocene basins nucleated both within the betic cordillera e g alboran sea and in its foreland valencia and provencal troughs the n40 70 direction of grabens is oblique to the coexisting n60 80 trending orogen and shows its structural independence from the orogenic roots thus as the extension cross cuts the orogen and developed also well outside the thrust belt front the westernmost basins of the mediterranean had to develop independently from the alps betics orogen therefore the alboran extension considered a classic example of a basin generated by the collapse of an orogen cannot be ascribed to the detachment or annihilation of the lithospheric root in contrast with the eastward migrating extensional basins the betic balearic thrust front was migrating westward producing interference or inversion structures

records of precambrian early palaeozoic volcanic and sedimentary processes in the central european variscides a review of shrimp zircon data from the kaczawa succession sudetes sw poland abstract the early pre orogenic stages of evolution in the variscan belt i e rifting processes opening of sedimentary basins and associated igneous activities are often obscure because many successions have yielded little or no biostratigraphic data have a strong metamorphic overprint and are tectonically deformed and dislocated the increasing application of shrimp zircon dating has provided useful constraints on magmatic and metamorphic processes helped locate probable source areas for detritus within sedimentary successions and facilitated large scale palaeogeographic correlations this methodology has recently thrown considerable light on the age and relationships of the previously poorly constrained rock units of the kaczawa complex in the polish west sudetes thus recent shrimp studies in the kaczawa mountains have yielded early ordovician ages of the initial rift type bimodal volcanic suites at the bottom part of the kaczawa succession c 503 ma for metarhyodacites of crustal derivation and c 485 ma for alkaline metatrachytes of mantle signature these dates provide a firm temporal constraint on the initial rift magmatism interpreted as related to the continental break up of the northern peripheries of gondwana new shrimp data from metavolcaniclastic and metasedimentary rocks of the kaczawa complex have yielded results that have provided significantly changed interpretations on their age and relationships for instance a siliciclastic sequence interpreted as belonging to the lower part of the kaczawa complex the gackowa sandstones and seemingly sourced using an array of geochemical and mineralogical evidence from nearby early ordovician volcanic rocks has surprisingly yielded zircon ages not younger than precambrian and thus this unit has tentatively been reinterpreted as a possible correlative of the neoproterozoic lusatian graywackes felsic metavolcaniclastic rocks embedded in the carbonate succession of the wojcieszow limestone have yielded shrimp zircon ages of c 497 ma thus supporting a late cambrian early ordovician age for this shallow water limestone sequence which had been proposed to be late ordovician silurian or younger in age based on controversial foraminifera evidence and more recently assigned to the mid cambrian based on newly found archaeocyathid fragments and age spectra of zircon populations in the metamudstone sequence of the radzimowice slates of thus far enigmatic stratigraphic position indicate that these deposits may have accumulated during early palaeozoic rifting with source areas similar to those known from parts of gondwana e g nw africa overall the new shrimp zircon studies both in metavolcanic and metasedimentary sequences have considerably illuminated their affinities and should provide encouragement for further application of this technique in this region in general the results provide support and detail for interpretation of this rock complex as reflecting the early stages of development of the volcanic and sedimentary processes operating along north gondwana during latest precambrian and early palaeozoic times

ordovician passive continental margin magmatism in the central european variscides u pb zircon data from the se part of the karkonosze izera massif sudetes sw poland approximately 500 ma old orthogneisses are widespread in the eastern part of the variscan belt and are commonly interpreted to have intruded mica schist series of assumed neoproterozoic age new shrimp zircon ages of quartzofeldspathic metavolcanogenic rocks of the mica schist series in the eastern part of the karkonosze izera massif sw poland indicate that they are late cambrian early ordovician rather than neoproterozoic in age based on the zircon age spectra distributed mainly between ca 500 and 660 ma with a few proterozoic inherited minimum ages of ca 970 and 1 825 ma younger zircon dates dispersed between ca 412 and 464 ma are interpreted as a result of pb loss likely caused by subsequent metamorphism consequently the felsic metavolcanogenic rocks appear to be roughly contemporaneous with the intrusion of ca 500 ma old orthogneiss protoliths with the pooled concordia age of 487 8 ma interpreted as the best approximation of the protolith intrusive age field relationships petrological and geochemical features of the felsic and mafic rocks studied support a model in which the accompanying mica schist series are not the original country rocks to the ca 500 ma granite intrusions and indicate that their recent close proximity is the result of tectonic juxtaposition however both the mica schists enclosing the bimodal metavolcanic rocks and the orthogneisses are interpreted to represent a cambro ordovician passive continental margin sequence being part of the saxothuringian domain they are tectonically overlain to the east by hp t metamorphic units comprising morb type metaigneous rocks and delineating a tectonic suture separating the saxothuringian block in the west from an assumed continental block tepla barrandian to the south east

the palaeozoic variscan oceans revisited abstract geological evidence supported by biogeographical data and in accord with palaeomagnetic constraints indicates that one ocean models for the variscides should be discarded and confirms instead the existence of three gondwana derived microcontinents which were involved in the variscan collision avalonia north armorica franconia and thuringia subdivided by a failed vesser rift and south armorica central iberia armorica bohemia all divided by small oceans in addition parts of south eastern europe including adria and apulia are combined here under the new name of palaeo adria which was also peri gondwanan in the early palaeozoic oceanic separations were formed by the break up of the northern gondwana margin from the late cambrian onwards most of the oceans or seaways remained narrow but much like the alpine cenozoic oceans gave birth to orogenic belts with hp uhp metamorphism and extensive allochthons the saxo thuringian ocean between north and south armorica and the galicia moldanubian ocean between south armorica and palaeo adria only the rheic ocean between avalonia and peri gondwana was wide enough to be unambiguously recorded by biogeography and palaeomagnetism and its north western arm closed before or during the emsian in europe ridge subduction under the northernmost part of armorica in the emsian created the narrow and short lived rheno hercynian ocean it is that ocean and not the rheic whose opening and closure controlled the evolution of the rheno hercynian foldbelt in south west iberia south west england germany and moravia czech republic devonian magmatism and sedimentation set within belts of early variscan deformation and metamorphism are probably strike slip related the first arrival of flysch on the forelands and or the age of deformation of foreland sequences constrains the sequential closure of the variscan seaways galicia moldanubian in the givetian saxo thuringian in the early famennian rheno hercynian in the tournaisian additional mid to late devonian and partly early carboniferous magmatism and extension in the rheno hercynian saxo thuringian and galicia moldanubian basins overlapped with variscan geodynamics as strictly defined the early carboniferous episode was the start of episodic anorogenic heating which lasted until the permian and probably relates to tethys rifting

u pb dating of serpentinization hydrothermal zircon from a metasomatic rodingite shell sudetic ophiolite sw poland abundant zircon grains were found within a metasomatic chlorite corrensite trioctahedral regularly interstratified chlorite smectite shell that surrounds rodingite from the jordanow gogolow jg serpentinite massif sudetic ophiolite bohemian massif the zircon grains bear two types of primary fluid inclusions containing either liquid co2 or aqueous solutions the inclusions were used to assign the p t conditions of the zircon formation 270 300 c ca 1 kbar using the crossed isochore method abraded single zircon grains give a u pb age of 400 4 3 ma which is interpreted as the age of zircon crystallization this zircon formed during rodingitization i e a metasomatic process directly connected with the serpentinization and thus provides the opportunity of direct dating of the early serpentinization process the zircon age from the jordanow gogolow massif is consistent with the crystallization age of metagabbro protoliths from the sudetic ophiolite as determined by oliver et al j geol soc lond 150 1993 355 a ce anomaly combined with the mineralogical record of greenschist facies metamorphism of the mafic rocks from sudetic ophiolite suggests that the sm nd whole rock isotopic data of pin et al lithos 21 1988 195 353 21 ma possibly characterize the age of later metamorphic event

structural evolution of the pematang reservoirs kelabu dingga gas fields sumatra the kelabu jingga area located in the kiri trough of the central sumatra basin produces gas from the paleogene pematang group the pematang group consists of sandstones claystones organic rich shales and conglomerates deposited in fluvial and fresh water deltaic and lacustrine environments deposition occurred during regional tectonism associated with a major plate reorganization in the pacific and indian oceans during the paleogene subsequent rifting and basin development occurred in the kiri trough area in central sumatra syngenetic listric faults and associated rollover folds formed during rifting the pematang group was deposited in deep transtensional pull apart grabens and shallow extensional rifts tectonics strongly influenced the geometry and lateral continuity of the fluvial deltaic sands during the neogene oblique convergence of the indian ocean plate with the asian plate resulted in a regional dextral wrenching event in the central sumatra basin that overprinted the earlier extensional style of faulting in the kiri trough both extensional and compressional features are evident interpretation of a 3d seismic survey wireline logs including dipmeter and fms data and core data has delineated fault styles and depositional trends within the pematang group in the kelabu jingga fields the resultant maps and cross sections reveal hydrocarbon reserves and new drilling opportunities

late middle miocene volcanism in northwest borneo southeast asia implications for tectonics paleoclimate and stratigraphic marker abstract explosive volcanic events often produce pyroclastic materials that can be recognized from the geological record these discrete pyroclastics form regional marker beds here we report the occurrence of a tephra layer interbedded within very thick coal beds near mukah sarawak borneo traceable for tens of kilometers in the mukah area of sarawak this tephra layer can be considered as regional stratigraphic marker with precise chronostratigraphic control systematic sedimentological mineralogical geochemical and zircon u pb geochronological studies have revealed a major effusive volcanic event during the latest middle miocene presumably contemporaneous and or related to a magmatic event of an earlier phase of the mt kinabalu pluton or magmatism in west sarawak or east sabah the volcanic event had promoted catastrophic flooding of coastal swamps and fall out from the ash clouds that formed a regionally monotonous tephra layer across the serravallian tortonian boundary in conjunction with the regional occurrences of trap rocks structural trends and known tectonic events we constrained the regional depositional environments and climate the tephra layer was deposited in a coastal plain swamp seasonal shallow high moderate energy fluvial channel lacustrine environmental setting wherein atmospheric fallout and eroded material from regoliths formed over older basement and volcanic rocks of the hinterland which were mixed to produce the tephra layer this tephra layer is sandwiched between the very thick coal beds a pre existent volcanic chamber that was active for a long time also experienced periodic explosive activity from probably the same magma chamber and conduit and including a major explosive activity that recycled early formed crystals and felsic magma rhyolite dacite during the major effusive event are also recognized our findings provide robust evidence for the prevalence of intensive chemical weathering under a wet humid climate and relative tectonic quiescence before the major effusive event and the existence of vast monotonously gently sloping coastal plains and luxuriant vegetation akin to the present

equatorial weathering landform development and the formation of white sands in north western kalimantan indonesia abstract the morphology and geochemistry of weathering profiles in miocene granodiorites from the coastal lowlands of nw kalimantan indonesia 1 n lat indicate long term weathering rates landform development and mechanisms for the formation of white sands found widely in valleys and depressions samples are analysed from convex hill piedmont glacis and valley slope profiles all profiles above the saturated zone are strongly gibbsitic but kaolinite minerals are dominant below the water table the profiles are interpreted as expressions of the perhumid equatorial climate rainfall 3000 mm y 1 acting within a dynamic regime of landscape lowering during the neogene the current profiles being largely quaternary 0 4 0 6 ka possible effects of quaternary tectonic and environmental changes are considered including those caused by a late pleistocene drier climate when there was greater water table fluctuation and surface erosion landform evolution is a form of dynamic etchplanation with a long term rate of landscape and weathering profile lowering of ca 50 mm ka 1 within this regime some of the white sands may be residual weathering products locally redistributed by colluvial or alluvial processes they originated in the podzolising environment of the weathering profile and later experienced post depositional diagenetic changes within the hydromorphic regime of the valley floor

u pb ages from sw poland evidence for a caledonian suture zone between baltica and gondwana faunal and palaeomagnetic evidence suggests the existence of a c 3000 km wide tornquist sea between gondwana and baltica in early ordovician times which narrowed to 50 2 ma an unmetamorphosed ophiolite gives a 420 20 2 ma age whilst in two other terranes amphibolite facies island arc lavas have fossiliferous lower ludlow 424 415 ma sequences all are unconformably overlain by unmetamorphosed upper devonian conglomerates a sinistral transpressive regime is observed in regionally extensive mylonite zones titanite and zircon ages 338 2 3 and 339 4 ma record variscan magmatism the data suggest considerable narrowing of the tornquist sea during the ordovician continuing ocean floor and island arc activity in the silurian and final sinistral transpressive closure by the mid devonian

zircon shrimp u pb ages and in situ hf isotopic analysis for the mesozoic intrusions in south taihang north china craton evidence for hybridization between mantle derived magmas and crustal components abstract the north china craton ncc was stabilized in paleo proterozoic times and the eastern part of it was remobilized in the mesozoic as is indicated by the presence of voluminous mesozoic magmas in eastern ncc in particular the lithospheric mantle beneath eastern ncc was significantly thinned during the intense mesozoic tectono magmatic activity which makes the ncc different from most other ancient cratons the mesozoic magmas may thus provide crucial evidence regarding the processes that transformed the ncc from craton to a tectonically active region the south taihang magmatic complex lies in the western part of the mesozoic magmatic zone in the ncc the complex falls into three main plutonic rocks the hongshan syenite the xishu gabbroic diorite monzonite and the wu an monzonitic rocks zircon u pb dating reveals that the three plutonic rocks were emplaced contemporaneously at 132 ma in situ hf isotopic analyses for the dated zircons indicate that the hongshan syenites show homogeneous hf t values 10 to 13 which are slightly lower than those 9 0 for the enriched subcontinental lithospheric mantle sclm as revealed by zircons from mafic rocks that originated from melting of sclm this suggests that the parental magma to the syenites was likely derived from melting of the enriched sclm and contaminated slightly by old lower continental crustal material during ascent the xishu and wu an gabbroic diorites to monzonitic rocks however show significantly varied hf isotopic compositions with hf t 9 2 to 16 and 15 5 to 24 respectively the wide range of hf t values for a single sample suggests that the xishu and wu an plutons formed through a process of hybridization between enriched mantle derived mafic magma and crustal components in variable proportions this is supported by the textural and compositional disequilibrium of plagioclase phenocrysts from the two plutons the wu an monzonitic rocks show lower hf t values than the xishu gabbroic diorite monzonite suggesting more incorporation of crustal components in the source the sudden surge of magmatic activity in the south taihang orogen took place as a result of lithospheric extension that caused partial fusion of the enriched portions of sclm generating voluminous mafic magmas underplating of the mafic magmas in the lower crust consequently caused partial melting of the old basement rocks to produce granitic melts which was followed by mixing between the mafic and granitic magmas

palaeocene early eocene inversion of the phuquoc kampot som basin se asian deformation associated with the suturing of luconia abstract the little explored cambodian and vietnamese phuquoc kampot som basin is a late jurassic to early cretaceous foreland basin developed in response to the build up of a palaeo pacific magmatic arc a combination of seismic data well data and outcrop geology complemented by fission track and u pb analysis is used to unravel the basin history this reveals a hitherto unknown earliest palaeogene basin inversion associated with the luconian suturing to se asia and the shutdown of palaeo pacific subduction underneath se asia the phuquoc kampot som basin and the khorat basin in thailand constitute the erosional remnants of a larger basin that covered large parts of se asia in late mesozoic time and subsequently became segregated during earliest palaeogene inversion and erosion inversion was focused along the several hundred kilometres long kampot and khmer chanthaburi fold belts that confine the phuquoc kampot som basin and merge with the mae ping and the three pagodas fault zones these connections together with local nw se trending sinistral transpressional faults offshore indicate a link between initial se asian left lateral strike slip faulting and the luconian suturing the separation between the once unbroken khmer chanthaburi fold belt and the phetchabun fold belt in thailand suggests a 50 100 km cenozoic left lateral offset across the mae ping fault zone

past environmental and circulation changes in the south china sea input from the magnetic properties of deep sea sediments abstract the south china sea located at the transition between the pacific and the indian ocean receives every year mainly during the rain season enormous amounts of river sediments originating from the erosion weathering of rocks in the catchment basins at sea these sediments are carried by different water masses to their deposition site and they constitute a unique archive for past environmental studies in this region the magnetic fraction of deep sea sediments though forming a minority in volume provides incredibly valuable information for paleoceanographic reconstructions as long as its provenance and source to sink processes are well constrained after a brief description of the climatic sedimentological and oceanographic context of the south china sea scs a review of the information available so far in the literature about the magnetic properties of scs sediments is presented it shows a large variety of interpretations conclusions that finally results in a rather unclear picture because in such a context the characterization of the sediment at the source is critical the magnetic properties recently obtained from a set of samples from rivers and marine surface sediments are summarized to describe the present day situation they are then used to interpret paleorecords from a set of seven marine cores distributed from the southern to the northern basins at different water depths and all covering at least the last climatic cycle the results reported here for the first time suggest that the magnetic mineralogy remains rather stable in time on land and that its time and spatial distribution at sea is an interplay of changes in sea level and deep sea circulation during low sea level periods bottom deep sea circulation is weak and the deposited sediment originates from the proximal rivers on the contrary during high sea level the circulation is enhanced transporting more sediment most likely from taiwan and luzon to the northwestern part of the scs and also in smaller proportion to the southern basin where it mixes with the local river borne sediment by comparing the two longest records we observe that this pattern is repeated over the last 900 ka superimposed to the 100 kyr cyclicity we also observe a longer term evolution with a maximum in the bottom current strength around 500 ka coinciding with global changes in the deep ocean circulation and carbon cycle these new results based on a wide spectrum of magnetic properties of numerous marine sedimentary cores from the scs show that the magnetic fraction yields important insights into past changes of the sedimentary pathways in particular the dynamic of the deep sea circulation depending on the global climatic context

the izera metabasites west sudetes poland geologic and isotopic u pb zircon evidence of devonian extension in the saxothuringian terrane abstract in the lausitz izera massif of the saxothuringian terrane part of the central european variscides 515 480 ma metagranites have been intruded by a swarm of basic veins that have within plate alkali basalt geochemistry or rarely normal mid ocean ridge basalt n morb geochemistry based on their spatial orientation distribution in the region and structural relationships to the host metagranites these basic veins could be grouped into three types that displayed six varieties of host vein contacts zircons extracted from eight of the basic veins revealed that there were two populations clear zircons and brown zircons each type were subjected to both single grain conventional u pb analysis and to sensitive high resolution ion microprobe shrimp u pb analysis the clear grains yielded ages 480 ma clustering at 500 ma the brown grains yielded ages between 390 and 365 ma clustering at 370 ma the colourless zircons possess an oscillatory zoned structure and rare earth element ree distribution pattern that suggests they come from the host granites and from deeper neoproterozoic granitoid basement however the basic host rocks show almost no obvious contamination by felsic material the turbid brown grains which are dark under cathodoluminescence also seem to be mainly magmatic because of their internal structures high th u ratios and ree pattern when the zircon results are integrated into the regional geology an 30 m y period of episodic intra plate predominantly alkaline basic magmatism at the passive margin of the saxothuringian terrane is suggested with maximum activity at 370 ma during an extensional regime combining the factors of the relatively high thermal gradient during early metamorphism of the metabasites 450 c 2 kbar the geology of saxothuringia and the regional structural data we propose a plume model of hot fingers type whereby the basic magmatism of the izera region was due to repeated devonian intrusions derived from garnet bearing enriched oib type and less commonly depleted asthenosphere sources the waning stages of this activity were coeval with the early deformation of the izera granite host basic vein system and matched by rifting and extensional widening of the saxothuringian basin in its izera kaczawa segment

characteristics of atmospheric dust deposition in snow on the glaciers of the eastern tien shan china wind blown mineral aerosol dust derived from the crustal surface is an important atmospheric component affecting the earth s radiation budget deposition of water insoluble dust was determined in snow deposited on urumqi glacier no 1 haxilegen glacier no 51 and miaoergou glacier eastern tien shan china analysis of the horizontal distribution of snow depth and concentration and flux of dust particles in the snow cover suggests that dust deposition differs on each of these glaciers as the atmospheric environment changes from west to east mean mass concentrations of micro particles in the size range 0 57 26 mm diameter at the three locations are respectively 969 1442 and 3690 m gk g 1 with an increasing trend from west to east dust layers in the snow cover contain na and ca rich materials typically found in central asian dust particles volume size distributions of dust particles in the snow showed single modal structures having volume median diameters of 3 22 mm dust profiles in the snow cover over the past 4 years reveal frequent sporadic high dust concentrations with a large year to year variability implying that dust deposition in the eastern tien shan is very sensitive to atmospheric environment change

a structural model for the western central sudetes a deformed stack of variscan thrust sheets a model based on new structural and geochemical data is presented it unifies the structural history of the izera rudawy janowickie and kaczawa complexes with the fore sudetic block despite their current separation by the intra sudetic and marginal sudetic faults above the granitoid izera kowary and w droze gneisses at the base of the structural sequence the ductile kowary shear zone marks the basal decollement of the wierzawa thrust sheet comprising often highly strained metasediments associated with enriched tholeiitic and alkaline metabasites above it the ductile kaczorow shear zone corresponding to the main mylonitic zone within the leszczyniec shear zone in the rudawy janowickie complex marks the base of the dobromierz thrust sheet characterized by voluminous morb like meta tholeiites and minor metasediments in the higher parts of the rudawy janowickie and kaczawa complexes and the pyszczynska hill area of the fore sudetic block in the east the sleza ophiolite and the gory sowie block override the entire nappe stack kinematic fabrics in the major and related shear zones indicate d 1 compressional transport towards the northwest followed by minor d 2 extensional movements the thrust stack was deformed during d 3 by southwest verging folds was subsequently intruded by post orogenic granites and later disrupted by the intra sudetic marginal sudetic and associated faults

the tepla saxothuringian suture in the karkonosze izera massif western sudetes central european variscides the southern and eastern karkonosze izera massif northern bohemian massif exposes blueschist facies rocks and morb type magmatic complexes during late devonian to early carboniferous times these were overthrust within a nappe pile toward the nw onto the pre variscan saxothuringian basement composed of the izera kowary metagranitoids and their envelope the lowermost nappe or parautochthonous unit of the pile is the low grade metamorphosed jest d complex comprising a devonian to early carboniferous sedimentary succession of the saxothuringian passive margin this is tectonically overlain by the south karkonosze complex which represents ordovician silurian volcano sedimentary infill of the saxothuringian basin affected by late devonian hp metamorphism the uppermost nappe is the early palaeozoic epidote amphibolite grade leszczyniec morb like complex cropping out on the eastern margin of the karkonosze izera massif it probably represents a fragment of obducted saxothuringian basin floor the nappe pile was stacked beneath the overriding upper plate margin now concealed below the intra sudetic basin and hypothesized to represent a fragment of the tepla barrandian terrane the nappe stacking triggered by buoyancy controlled upward extrusion of the subducted continental slab was the main mechanism for the exhumation of hp rocks the final stages of the nw ward nappe stacking were accompanied and followed by se directed early carboniferous extensional collapse the lower plate of the suture zone was uplifted at that time and intruded by the 330 ma old nearly undeformed karkonosze granite pluton as a result of the collapse the tepla barrandian upper plate was downthrown on shear zones and brittle faults and buried under several km thick synorogenic late tournaisian through namurian and post orogenic late carboniferous early permian succession of the intra sudetic basin the south and east karkonosze suture most probably is a fragment of the tepla saxothuringian munchberg tepla suture belt known from the western bohemian massif

geochronology and nd sr systematics of lusatian granitoids significance for the evolution of the variscan orogen in east central europe a variety of pre variscan granitoids and two variscan monzogranites occurring in the central and western parts of the lusatian granodiorite complex lgc saxonia were dated by the single zircon evaporation method complemented by whole rock nd isotopic data and rb sr whole rock and mineral ages the virtually undeformed pre variscan granitoids constitute a genetically related mostly peraluminous magmatic suite ranging in composition from two mica granodiorite muscovitebearing biotite quartz diorite tonalite and granodiorite to biotite granodiorite and monozogranite

neotectonic regime on the passive continental margin of the northern south china sea abstract between 1989 and 1994 more than 6600 km of reflection seismic profiles were obtained in the south china sea off hong kong with the german research vessel sonne during cruises so 50b so 72a and so 95 a seismo stratigraphic interpretation of this data set leads to a new age assignment of the unconformity t0 which we place within the pleistocene both neogene unconformities t1 and t0 are generated by uplift of the dongsha rise and truncation of their overlying strata this uplift is caused by intrusion of magma into the upper crust our seismic profiles show plutons which have penetrated the sedimentary cover whereby their original stratification in the contact zone is eliminated these magmato tectonic events may be correlated to the two main collision phases between taiwan and the continental margin of east china 5 3 and 3 0 ma ago the collisional events subsequent to the nnw to wnw drift of taiwan transformed the compression into strike slip movements along the continental margin of southeastern china the accompanying stress regime is transtensional with subsidence of the cooling oceanic crust since the cessation of rifting and its consumption beneath the manila trench providing the extensional stress the strike slip movements remobilized many of the rift and drift faults providing pathways for magma ascent the tectonic framework of the northern south china sea is characterized by miocene faults trending ne sw these faults are scarce but are distributed throughout the study area pliocene faults striking ene wsw to ne sw are concentrated west of the dongsha islands and are mostly strike slip in character recent faults are generally oriented ne sw subparallel to the synrift faults they result in part from local uplifts where they are normal in character but strike slip motion also occurs most of the faults involve the basement and represent reactivated zones of weakness of the rift and drift phases

a triassic to cretaceous sundaland pacific subduction margin in west sarawak borneo metamorphic rocks in west sarawak are poorly exposed and studied they were previously assumed to be pre carboniferous basement but had never been dated new 40ar 39ar ages from white mica in quartz mica schists reveal metamorphism between c 216 to 220 ma the metamorphic rocks are associated with triassic acid and basic igneous rocks which indicate widespread magmatism new u pb dating of zircons from the jagoi granodiorite indicates triassic magmatism at c 208 ma and c 240 ma u pb dating of zircons from volcaniclastic sediments of the sadong and kuching formations confirms contemporaneous volcanism the magmatic activity is interpreted to represent a triassic subduction margin in westernmost west sarawak with sediments deposited in a forearc basin derived from the magmatic arc at the sundaland pacific margin west sarawak and nw kalimantan are underlain by continental crust that was already part of sundaland or accreted to sundaland in the triassic one metabasite sample also previously assumed to be pre carboniferous basement yielded early cretaceous 40ar 39ar ages they are interpreted to indicate resumption of subduction which led to deposition of volcaniclastic sediments and widespread magmatism u pb ages from detrital zircons in the cretaceous pedawan formation are similar to those from the schwaner granites of nw kalimantan and the pedawan formation is interpreted as part of a cretaceous forearc basin containing material eroded from a magmatic arc that extended from vietnam to west borneo the youngest u pb ages from zircons in a tuff layer from the uppermost part of the pedawan formation indicate that volcanic activity continued until c 86 to 88 ma when subduction terminated

systematics of internal zircon morphology in major variscan granitoid types the internal morphologies of zircon crystals from different types of granitoids alkaline calcalkaline and anatectic are revealed by cathodoluminescence imaging and are described in terms of growth rates of the crystal faces relative to each other zircons in the alkaline granitoids are characterized by high and constant growth rates of 010 relative to the pyramidal forms and by symmetric grwoth of 011 zircons in the calcalkaline and anatectic granitoids are characterized by fluctuating or gradually decreasing relative growth rates of 010 by asymmetric and highly variable growth of 011 and by a tendency of 110 to become grwoth inhibited corrosion events are interspersed during zircon growth in the calcalkaline magmas in the calcalkaline and anatectic magmas a discontinuity breaks the morphological evolution at late stages of crystallization the discontinuity coincides with a sharp drop in cathodoluminescence the growth behaviour of each crystal form is analysed and compared with predictions made by the periodic bond chain pbc theory it is argued that the relative growth rate of 010 depends on supersaturation that the growth rates of 011 faces are changed in response to different ratios of adsorbing cations na k al and that 110 faces become growth inhibited by the adsorption of h2o or trace elements enriched in the residual liquid morphological and chemical discontinuities at late stages of crystallization are reasonably explained by the formation of larger growth units from smaller ionic entities in the residual liquid important factors controlling the zircon morphology in different types of granitoids are high cooling rates alkaline magmas magma mixing calcalkaline magmas enrichment of h2o and trace elements in residual liquids calcalkaline and anatectic magmas and the major element chemistry of the magma possibly the ratio of na and k to al agpaicity

formation of arcs and backarc basins inferred from the tectonic evolution of southeast asia since the late cretaceous abstract results of the geological and geophysical surveys in the daito ridges and basin in the northern west philippine basin suggest that the daito ridge was an arc facing toward the south from the late cretaceous to the early tertiary the late cretaceous and tertiary history of southeast asia is evaluated based on these data in the daito ridges and basins and reconstructed based on overall plate kinematics that have operated in this area during the late cretaceous the daito ridge and the east philippine islands were positioned along the boundary between the indian and pacific plates the western half of the philippines setting on the indian plate approached from the south and collided with the east philippine daito arc either during the latest paleocene or the earliest eocene it is inferred that the bulk of the philippine archipelago rotated clockwise and borneo spun counterclockwise during the tertiary from the reconstruction the formation of backarc basins and their spreading direction are assessed as a result some primary causes and significant characteristics are suggested for the opening of backarc basins in southeast asia first opening of some backarc basins commenced with or was triggered by collisions second backarc basins opened approximately parallel to oceanic plate motion third the formation of some backarc basins was triggered by the approach of a hot spreading center fourth the spreading mode or direction of backarc basins was greatly affected by the configuration of the surrounding continent and was also rearranged to spread approximately parallel to oceanic plate motion the formation of backarc basins and their spreading direction can be reasonably explained by plate kinematics however the generative force responsible for their formation is possibly within the subduction system particularly to form horizontal tensional force in backarc side

paleomagnetism of borneo abstract the paleomagnetism of borneo remains controversial although the preponderance of results both from the island itself and from the surrounding regions suggest that counterclockwise ccw rotation has taken place ccw rotations are seen in minor intrusions in sarawak sabah and kalimantan which increase systematically with the age of the intrusion to a maximum value of 51 8 3 7 the rotation can be no older than 25 ma which is the age of the intrusion showing the maximum rotation the rotation appears to have neared completion by 10 ma similar ccw rotations are seen in sites from peninsular malaysia through borneo to sulawesi the celebes sea and palawan in the philippines but the ages of these rotations are for the most part unknown in mesozoic rocks in kalimantan and sarawak a stronger declination rotation of nearly 90 ccw is recorded at seven sites including sites which pass fold and reversal tests this strong rotation is no older than youngest cretaceous and although seen over a wide region in borneo it is not seen in peninsular malaysia nor in the celebes sea or palawan where only the weaker ccw rotation is seen the widespread occurrence of this strong rotation in western borneo suggests that it is essentially a rigid plate or microplate rotation and not a series of local rotations caused by distributed shear in limited deformation zones the rotation of borneo appears to be a consequence of convergence between the australian and eurasian plates which is accommodated by subduction along the northwest margin of borneo

evidence of multiphase deformation in the rajang crocker range northern borneo from landsat imagery interpretation geodynamic implications comment 1 abstract landsat imagery structural analysis and nannoplankton dating of the rajang crocker belt in northern borneo defines the geometry style and timing of the development of various tectonostratigraphic units these data are integrated with a review of the formations of the area in order to to emphasize the palaeogeographic environments of the units in sarawak the trends are essentially e w with a first event being characterized by strong deformation and schistosity which affects upper cretaceous lower eocene terrigeneous units prior to the deposition of the middle upper eocene a second event is marked by the northward thrusting of eocene rocks over the oligocene prior to the deposition of the middle miocene succession in the crocker belt of sabah two oblique generations of structures can be observed these deformations occurred prior to the deposition of the upper middle miocene tight or even reverse folds with n s trending axes are deformed by large folds with associated thrusts the axes of these last structures trend n s in the brunei area n60e in northern sabah and bend towards n130e in the sandakan area this complex pattern has been affected by late n60e trending normal faults in central sabah

cenozoic plate reconstruction of the south china sea region abstract reconstructions of the south china sea region at 60 ma 40 ma 30 ma 20 ma 10 ma and 5 ma are presented we have attempted to place the south china sea basin in a regional tectonic framework the tectonic evolution of the major blocks surrounding the south china sea were analyzed as well as the relative motions of the indian and australian plates we have tried to correct the tectonic models available in this region a 3 d graphics terminal was used to derive rotation poles for the different tectonic blocks and our model was then tested to determine its self consistency when the model conflicted with previous interpretations the input data were evaluated for alternative explanations at least two and possibly three stages of extension can be recognized in this region the earliest one active in the late cretaceous to eocene involved nw se extension the second one active from the late eocene to early miocene involved north south extension the third stage of extension which probably trended nw se can be dated as post oligocene the first extensional event produced the ne sw trending proto south china sea and a series of sedimentary basins along the south china margin following the southeastward extrusion of indochina the proto south china sea was mostly consumed at the palawan trough renewed north south extension in the south china continental margin started the present day south china sea spreading in the oligocene the southeastward extrusion of indochina blocked by sundaland resulted in the nw se trending opening of the south china sea basin in the early miocene collision of the north palawan microcontinental block with the west philippines block stopped the opening of the south china sea at the end of early miocene spreading activity switched to the sulu sea basin in the middle miocene but collision between the sulu ridge and the west philippines at mindanao halted the opening of the sulu sea at the end of the middle miocene in the late miocene greater india continued its northward path and seems to have ripped open the andaman sea in the pliocene subduction along the northern manila trench placed the north luzon arc on a collision path with the east asia continental margin at taiwan our reconstructions along with detailed geological and geophysical information may be used as a predictive tool for basin evolution models and block interactions in this region the development of the south china sea basin the gulf of thailand the malay basin and the central thailand basins are the result of collision induced extensional forces the sulu celebes and sumatra basins were formed as a consequence of prolonged subduction the opening of the pearl river mouth west natuna south china sea sulu and possibly celebes basins were terminated by various plate collisions during the course of plate reorganizations major boundary faults have changed their slip senses during different stages of evolution

provenance of the cretaceous eocene rajang group submarine fan sarawak malaysia from light and heavy mineral assemblages and u pb zircon geochronology abstract the rajang group sediments in central borneo form a very thick deep water sequence which was deposited in one of the world s largest ancient submarine fans in sarawak the lupar and belaga formations form the rajang group characterised by turbidites and large debris flows deposited in an interval of at least 30 ma between the late cretaceous maastrichtian and late middle eocene borneo is one of the few places in se asia where sediments of this age are preserved heavy mineral assemblages and detrital zircon u pb dating permit the rajang group to be divided into three units the schwaner mountains area in sw borneo and west borneo and the malay tin belt were the main source regions and the contribution from these source areas varied with time unit 1 of late cretaceous to early eocene age is characterised by zircon tourmaline dominated heavy mineral assemblages derived from both source areas unit 2 of early to middle eocene age has zircon dominated heavy mineral assemblages abundant cretaceous zircons and few precambrian zircons derived primarily from the schwaner mountains unit 3 of middle eocene age has zircon tourmaline dominated heavy mineral assemblages derived from both sources and reworked sedimentary rocks there was limited contemporaneous magmatism during deposition of the rajang group inconsistent with a subduction arc setting we suggest the rajang group was deposited north of the shelf edge formed by the lupar line which was a significant strike slip fault

geology sulfide mineralogy and petrogenesis of the angstberg ni cu pge sulfide mineralization lausitz block bohemian massif germany a potential ni cu exploration target in central europe abstract germany s largest known magmatic ni cu pge sulfide enrichment is associated with the gabbroic angstberg intrusion that is one of several small scaled ni cu sulfide bearing intrusions in the northern bohemian massif central european variscan belt the intrusions are part of a middle devonian to early carboniferous mafic ultramafic magmatic system that emplaced within cadomian granodiorites of the lausitz block the angstberg intrusion represents an exposed sub vertical dike like body 320 60 m in plan view and comprises olivine gabbronorite olivine gabbro gabbro olivine hornblende gabbro and hornblende pyroxene gabbro the hornblende bearing and hornblende free lithologies originate from at least two variably fractionated basaltic parental magma batches which differ in their ti lree hree and volatile contents fractionation probably took place in deeper seated sections of the magmatic system possibly within staging magma chamber s overall enriched incompatible trace element patterns suggest that the angstberg lithologies are linked with intra plate magmatism likely associated with a transtensional setting in the course of the variscan orogeny the previously suggested devonian age of the intrusion is confirmed by an 40ar 39ar biotite age of 373 4 0 9 ma for the olivine gabbro the magmatic sulfide mineralization is predominated by disseminated sulfides that are hosted in the olivine richest parts of the olivine gabbronorite and olivine hornblende gabbro lithologies in addition some sulfide matrix breccias up to 70 modal sulfides occur directly on the footwall contact of the intrusion to granodiorite both mineralization types are characterized by a predominance of pyrrhotite over pentlandite and chalcopyrite with minor secondary violarite and pyrite and accessory pge au and ag phases nickel rich bismuthotellurides of the melonite merenskyite solid solution series and froodite are the most common platinum group minerals disseminated sulfides are characterized by high ni moderate cu and low pt and pd tenors 4 9 wt ni 2 6 wt cu 200 800 ppb pt 200 1000 ppb pd sulfide matrix breccias feature comparable ni but lower cu pt and pd tenors 4 6 wt ni 0 3 1 wt cu 10 100 ppb pt 40 200 ppb pd fractional crystallization and wall rock assimilation of granodiorite are regarded as key factors for sulfide saturation in the magmas associated with the angstberg intrusion sulfur isotope compositions of pyrrhotite pentlandite chalcopyrite assemblages 1 4 to 0 2 vcdt propose a mantle origin of s whereas addition of crustal s cannot be completely ruled out as the s isotope values of the sulfides overlap with those of the granodiorite 7 to 4 vcdt olivine and sulfide textures suggest that disseminated sulfides likely originate from sulfide melts that were entrained in an olivine rich crystal mush during magma rise to upper levels the sulfide matrix breccias also resulted from entrained sulfide melts or from gravity driven downward percolation of sulfide melts from stratigraphically higher now eroded levels in both cases the formation of sulfide matrix breccias most likely was amplified by in situ thermomechanical erosion of the granodioritic wall rock caused by flash boiling of thermally dehydrating biotite despite spatial limitations of the mineralized zones and limited information about the architecture of the intrusions in the northern bohemian massif the angstberg intrusion as well as other neighboring magmatic sulfide occurrences may represent a new exploration target for ni and cu in central europe

dissolution reprecipitation of igneous zircon in mid ocean ridge gabbro atlantis bank southwest indian ridge abstract zircons recovered from oceanic gabbro exposed on atlantis bank southwest indian ridge typically display oscillatory and sector zoning consistent with igneous crystallization from mafic magmas in one rock of twenty investigated weak oscillatory zonation patterns are overprinted by secondary textural features characterized by mottled convoluted and wavy internal zonation patterns that are frequently associated with secondary micron to submicron scale micro porosity these zircons are hosted in a felsic vein that intruded an oxide gabbro both of which are cross cut by monomineralic amphibole and quartz rich veinlets zircons with weak oscillatory zonation patterns record a weighted average 206pb 238u age of 12 76 0 20 ma mswd 1 5 and have high trace element concentrations e g rees 0 4 2 2 wt y 0 6 2 8 wt p 0 4 0 9 wt and th u 0 1 0 5 these zircons are anomalously old 1 myr relative to the magnetic age for this portion of oceanic crust 11 75 ma in contrast zircons with non igneous secondary textures have a younger weighted average 206pb 238u age of 12 00 0 16 ma mswd 1 7 and have lower trace element concentrations e g rees 0 2 0 8 wt y 0 3 1 0 wt p 0 1 0 3 wt and slightly lower th u 0 1 0 3 the weighted average age of these zircons is similar to the magnetic anomaly age and other 206pb 238u ages of nearby rocks we do not observe a correlation between crystallographic misorientation internal texture or trace element chemistry we suggest that the decrease in trace element concentrations associated with the development of non igneous alteration textures is attributed to the purging of non essential structural constituent cations from the zircon crystal lattice at amphibolite facies conditions the mechanism of alteration re equilibration was likely an interface coupled dissolution reprecipitation processes that affected pre existing anomalously old zircons during shallow level magmatic construction of atlantis bank at 12 0 ma

late cretaceous to early tertiary structural elements of west kalimantan abstract recent geological and geophysical mapping in west kalimantan has allowed the definition of three domains with distinct geological and geophysical characteristics which were imprinted on the region by early cretaceous to eocene convergent tectonic events subduction related granitoids intruded low grade regional metamorphic rocks during the early cretaceous forming the schwaner mountains domain extending east west across the southern and central part of west kalimantan this is flanked in the northwest by a complex sequence of sedimentary and volcanic rocks ranging in age from late carboniferous to cretaceous which comprise the northwest kalimantan domain deformed cretaceous flysch deposits east of the northwest kalimantan domain form an accretionary complex representing the southern continuation of the extensive dominantly tertiary accretionary wedge in sarawak the boundary between the cretaceous accretionary domain and rocks of the northwest kalimantan domain is a fault which we interpret as a transform that marked the western limit of late cretaceous southward subduction beneath west kalimantan growth of the accretionary complex resulted in uplift of a ridge of melange and flysch deposits on which a half graben extensional basin formed and accumulated thick lacustrine deposits a sedimentary basin developed between continental rocks to the south and the emergent ridge comprising accretionary complex rocks and outer shelf deposits to the north in the position of a forearc basin as accretion proceeded the locus of underthrusting migrated northward and a second melange ridge and sedimentary basin developed farther to the north the evidence for accretionary processes and the association of these with sedimentary basin formation supports the hypothesis that an ancient south dipping subduction zone existed in the eastern part of west kalimantan during late cretaceous to early tertiary times

geochemical evidence for progressive rift related early palaeozoic volcanism in the western sudetes the volcanigenic rocks of the kaczawa mts western sudetes poland in the eastern variscides show changing geological and geochemical evolution during early palaeozoic time the lower part of the succession cambrian ordovician has three components 1 shallow marine to subaerial metabasalts associated with limestones and volcaniclastics the lavas are dominantly of a transitional tholeiitic alkaline type and their trace element patterns typically represent a rift related environment they pass laterally and upwards into more depleted basalts resembling enriched morb with nd isotopic characteristics indicating contamination by continental crust 2 interlayered rhyodacitic lavas and volcaniclastics which show negative nd values suggesting formation of the original magma by crustal melting 3 an overlying alkaline bimodal suite of lavas and volcaniclastic rocks as well as alkaline metabasites of shallow intrusive character the geochemistry of the latter resembles oceanic island volcanics but they may well have been emplaced in the same evolving rift environment the upper part of the kaczawa succession ordovician silurian in age comprises a thick and monotonous sequence of deep marine pillowed and massive metabasalts associated with black shales and cherts these lavas exhibit morb trace element characteristics with minor evidence of crustal contamination during this stage of rifting true oceanic crust probably formed it is thus suggested that the studied part of the kaczawa succession developed in a progressively evolving rift initially within an ensialic environment and finally reaching the stage of a basin underlain by oceanic type crust together with similar cambrian ordovician volcanic sedimentary associations widely distributed in western europe from portugal through france and germany they represent a record of the early palaeozoic rifting in the northern periphery of gondwana

adakites without a slab remelting of hydrous basalt in the crust and shallow mantle of borneo to produce the miocene sintang suite and bau suite magmatism of west sarawak abstract we present new geochronological and geochemical data for neogene magmatism from west sarawak zircon u pb geochronology divides neogene magmatic rocks of west sarawak into a lower miocene west sarawak sintang suite with ages of c 19 to 21 ma and a middle miocene bau suite with ages of c 12 to 14 ma magmatism occurred in multiple short lived pulses from approximately 24 ma and was coeval with magmatic activity in nw kalimantan and east kalimantan the majority of but not all bau suite samples display adakitic chemistry while the west sarawak sintang suite is predominantly non adakitic there was no active subduction zone or subducted slab associated with this adakitic magmatism instead the geochemical diversity is consistent with the bau and west sarawak sintang suites representing mixtures of mafic mantle derived magma with felsic magma derived from remelting of hydrous mafic rock that had been emplaced into the lithosphere of borneo as arc basalt tens or hundreds of millions of years previously this origin is most evident in the main sintang suite of central borneo kalimantan which has preserved less contaminated examples of the mafic endmember this endmember resembles basaltic rocks from several locations across borneo suggesting that intraplate mantle derived magmatism was responsible for remelting older hydrated basaltic rocks in the crust

deep seismic structure of the northeastern south china sea origin of a high velocity layer in the lower crust we present a 2 d seismic tomographic image of the crustal structure along the obs2012 profile which delineates the moho morphology and magmatic features of the northeastern south china sea margin the image was created by forward modeling rayinvr and traveltime tomographic inversion tomo2d overall the continental crust thins seaward from 27 km to 21 km within the continental shelf across the zhu i depression and dongsha rise with slight local thickening beneath the dongsha rise accompanying the increase in the moho depth the dongsha rise is also characterized by 4 7 km thick high velocity layer hvl 7 0 7 6 km s in the lower crust and exhibits a relatively high velocity 5 5 6 4 km s in the upper crust with a velocity gradient lower than those of the zhu i depression and tainan basin across the continental slope and continent ocean transition cot which contain the tainan basin the crust sharply thins from 20 km to 10 km seaward and a 2 3 km thick hvl is imaged in the lower crust we observed that volcanoes are located only within the cot but none exist in the continental shelf the dongsha rise exhibits a high magnetic anomaly zone and different geochemical characteristics from the cot based on those observations we conclude that the hvl underlying the cot is probably extension related resulting from the decompression melting in the cenozoic whereas the hvl beneath the dongsha rise is probably arc related and associated with the subduction of the paleo pacific plate these findings are inconsistent with those of some previous studies

structural styles and deformation fabrics of accretionary complexes intricately deformed stratally disrupted and mixed rocks produced at subduction zones have been considered structurally intractable however marine geophysical studies deep sea drilling analyses of subaerially exposed complexes and theoretical advances have recently produced breakthroughs in elucidating the structural enigmas of these accretionary complexes the penrose conference structural styles and deformational fabrics of accretionary complexes assembled specialists from the above and related research areas and addressed the research frontiers of this dynamic topic this conference in eureka california in may 1984 drew participants from great britain france canada japan and new zealand

imaging a mantle plume beneath the french massif central abstract teleseismic tomography is now widely recognised as a very powerful tool for studying the velocity structure of the lithosphere asthenosphere system on both local and regional scales a prime objective is to identify velocity perturbations and to constrain their location and intensity here we use the arrival times of p waves from teleseismic events recorded by a dense network of mobile and permanent stations within the french massif central to derive a 3d p velocity model for an area of 425 km 300 km combined with knowledge of the basement geology of the area and the timing and geochemical characteristics of tertiary quaternary volcanic activity we consider that the velocity model provides unequivocal evidence for the ascent of a thermally and chemically anomalous mantle plume beneath the massif central during tertiary times our model is consistent with regional bouger gravity anomalies documented patterns of neogene recent uplift and deformation fabrics within lithosphere derived mantle xenoliths exhumed by the volcanics

geochemistry and 40ar 39ar geochronology of the mafic metavolcanic rocks from the rýchory mountains complex west sudetes bohemian massif palaeotectonic significance the mafic metavolcanic rocks blueschists and greenschists of the r chory mountains crystalline complex west sudetes experienced sea floor hydrothermal alteration spilitization prior to regional metamorphism the metabasite geochemistry namely trace element and ree abundances indicates that the protolith was comparable in composition with 1 tholeiitic to transitional ocean floor basalts and 2 transitional and alkaline intra oceanic island basalts two main metamorphic events affected the r chory mountains metabasites in an earlier high pressure low temperature metamorphic event the rocks experienced blueschist facies metamorphism the results of 40 ar 39 ar geochronology studies on phengites from the mafic blueschists date the end of the earlier metamorphism to 360 ma the greenschist metamorphic overprint followed around 340 ma the elongated bodies of mafic metavolcanic rocks are situated within the prominent nne ssw leszczyniec shear zone following the trend of the r chory mountains and the rudawy janowickie mountains both the geochemical affinities and the blueschist facies metamorphism of the metabasites suggest that this shear zone evolved from the variscan suture dividing western and central terranes of the west sudetes according to the radiometric age for the end of the high pressure low temperature metamorphism the terranes accreted during the famennian a considerable time span between the formation of the metabasite protolith and the blueschist metamorphism may indicate long lasting subduction of a large oceanic plate between gondwana and laurussia possibly accompanied by terrane accretion prior to the variscan orogeny

geological development of the central and south vietnamese margin implications for the establishment of the south china sea indochinese escape tectonics and cenozoic volcanism abstract the vietnamese margin forms a key region to the understanding of escape tectonics and the development of the south china sea scs the existing geological reconstructions of the region are restricted to studies of single basins are based on limited amounts of geophysical data or analysis of onshore geological features these models are critically assessed on the basis of interpretation of the most comprehensive 2 d digital seismic database published to date within the area combined with a thorough analysis of existing literature and a new model is presented the vietnamese margin is underlain by a series of paleogene rift basins established through southeastward extrusion of indochina the east vietnam boundary fault evbf forms the almost 1000 km long seaward continuation of the left lateral ailao shan red river shear zone asrrsz toward the southern half of the phu khanh basin the evbf breaks up into discrete segments and splays into the se directed tua hoa fault zone paleogene faults splayed from the evbf and the mae ping shear zone and accommodated the coeval motion of these two major left lateral structural lineaments during the late oligocene basin inversions offshore occurred contemporaneously with initial right lateral inversion along the mae ping shear zone and the onset of major uplift of the metamorphic core complexes along the asrrsz it is suggested that a dramatic change of the regional stress pattern occurred in response to the northward movement of india and the effective coupling of the west burma block and india the later resulting in broadening of the indenting continental mass after the mid oligocene left lateral movements across the offshore evbf decreased and eventually ceased later onshore sinistral movements were accommodated by internal shortening and local clockwise block rotations within the shan thai terrain renewed rifting offshore south vietnam resulted from the jump of the scs spreading axis and subsequent neogene southwestward propagation of continental break up the neogene opening of the scs is viewed as a consequence of a slab pull associated with subduction of the proto scs underneath borneo as offshore neogene escape tectonism had virtually ceased during this phase of rifting right lateral transtension is inferred along n to nw oriented fault zones in the phu khanh and the nam con son basins rifting and by inference seafloor spreading continued until the end of middle miocene time although at significantly reduced rates during the final 5 10 ma termination of seafloor spreading is marked by a distinct latest middle miocene unconformity in the nam con son and the southern phu khanh basins neogene volcanism resulted in the build up of several magmatic structures across the central and south vietnamese margin and induced reactivation of older faults in the phu khanh basin the offshore magmatism heralded widespread volcanism onshore southern indochina associated with a latest neogene uplift and denudation event the uplift led to significantly increased siliciclastic accumulation rates offshore which repressed widespread carbonate deposition

glaucophane bearing assemblage overprinted by greenschist facies metamorphism in the variscan kaczawa complex sudetes poland an early palaeozoic ordovician metamudstone sequence near wojcieszow kaczawa mts western sudetes poland contains numerous metabasite sills up to 50 m thick these subvolcanic rocks are of within plate alkali basalt type primary igneous phases in the metabasites clinopyroxene salite and kaersutite are veined and partly replaced by complex metamorphic mineral assemblages particularly the kaersutite is corroded and rimmed by zoned sodic sodic calcic and calcic amphiboles the matrix is composed of actinolite pycnochlorite albite an 0 5 epidote ps 27 33 titanite calcite opaques and occasionally biotite phengite and stilpnomelane the sodic amphiboles are glaucophane to crossite in composition with nab from 1 9 to 1 6 they are rimmed successively by sodic calcic and calcic amphiboles with compositions ranging from magnesioferri winchite to actinolite no compositions between nab 0 92 and nab 1 56 have been ascertained the textures may be interpreted as representing a greenschist facies overprint on an earlier blueschist or blueschist greenschist transitional assemblage the presence of glaucophane and no traces of a jadeitic pyroxene quartz association indicate pressures between 6 and 12 kbar during the high pressure episode temperature is difficult to assess in this metamorphic event the replacement of glaucophane by actinolite chlorite albite with associated epidote allows restriction of the upper pressure limit of the greenschist recrystallization to 8 kbar between 350 and 450 c the mineral assemblage representing the greenschist episode suggests the p t conditions of the high pressure part of the chlorite or lower biotite zone the latest metamorphic recrystallization under the greenschist facies may have taken place in the visean

single zircon ages and whole rock nd isotopic systematics of early palaeozoic granitoid gneisses from the czech and polish sudetes jizerske hory krkonose mountains and orlice sněžnik complex granitoid orthogneisses make up the predominant rock type in the west sudetes from jizerske hory in the nw to the orlicke hory and sn nik mountains in the se these generally strongly foliated gneisses are calc alkaline in composition and display trace element characteristics suggesting generation in a volcanic arc setting single zircon ages reflecting the time of emplacement of the gneiss protoliths define a relatively narrow cambro ordovician range between 502 and 515 ma this is similar to previously reported zircon ages from the czech and polish west sudetes and documents an important and regionally extensive post cadomian magmatic event that we relate to continental arc magmatism on the margin of avalonia that developed during closure of the tornquist ocean an age of 492 ma for a microgranite dyke cutting deformed and metamorphosed orthogneisses in the orlicke hory shows the main deformation to be early paleozoic zircon xenocryst minimum ages range between 546 and 2070 ma and show maxima in the cadomian pan african 550 850 ma and grenvillian 1000 1300 ma time brackets the grenvillian event is also evident from nd mean crustal residence ages that vary between 1 34 and 1 87 ga from these data we suggest that the pre variscan granitoid gneisses of the czech west sudetes were largely generated by melting of a predominantly grenville age basement that was part of the northern margin of gondwana and may have been related to grenville age basement now identified in northern south america

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented

early palaeozoic initial rift volcanism in the central european variscides the kaczawa mountains sudetes sw poland evidence from sims dating of zircons early palaeozoic volcanic suites are widespread throughout the variscan belt and have commonly been ascribed to incipient rifting along the northern periphery of gondwana in cambrian to ordovician times their distribution across europe defines the present day extent of gondwana derived terranes and constrains the timing of their separation from the gondwanan margin the kaczawa mountains in the west sudetes at the eastern termination of the variscan belt include bimodal rift related rocks but their protolith age and hence their significance have been highly uncertain we have applied secondary ionization mass spectrometry zircon geochronology to a metarhyodacite and a metatrachyte from this suite yielding ages of 502 4 2 6 ma and 485 7 1 6 ma respectively this constrains the initial rift magmatism to c 500 485 ma in this part of the european variscides the rift related early palaeozoic volcanism thus seems to have been broadly synchronous throughout the peri gondwanan terranes of europe

the dual nature of the alpine himalayan system progress problems and prospects abstract two distinct groups of sutures belonging to two different orogenic complexes have been recognized within the alpine himalayan system associated with the development of the tethyan chains they are interpreted as places where two independent tethyan ocean complexes viz palaeo and neo tethys vanished during the permo carboniferous to early cretaceous and the late cretaceous to the present intervals respectively the older orogen is called the cimmerides and the younger the alpides cimmerides and alpides together constitute the super orogenic complex tethysides tethyside orogenic events also generated vast cratonic fields of deformation in eurasia until recently the recognition of these two orogenic complexes hidden within the alpine himalayan system had been hindered because of the artificial tripartite grouping of orogenic events of the phanerozoic into caledonian hercynian and alpine orogenic eras the most important current problems in the study of the tethysides are the relative importance of the various suture strands as sites of consumption of main tethyan oceanic branches the precise timing of ocean opening and closing along these sutures and the original provenance of the continental blocks constituting the tethyside orogenic collage a number of avenues of future research are suggested to tackle these problems