sm nd rb sr and u pb geochronology of a grenville terrane in southern mexico origin and geologic history of the guichicovi complex abstract the guichicovi complex forms the metamorphic basement near the western edge of the maya terrane in southern mexico petrographic field studies show that the guichicovi complex like other high grade metamorphic terranes in southern mexico consists of paragneisses and a igneous suite of rocks metamorphosed under granulite facies conditions the sm nd isotopic results yield depleted mantle model ages of 1 4 1 6 ga for the metaigneous rocks and of 1 5 2 0 ga for the metasediments on a sm nd isochron diagram the isotopic results of the metaigneous suite of rocks define an isochron whose slope corresponds to an age of 1 44 ga this age can be interpreted as the time of a major crust forming event discordant u pb zircon data from a felsic orthogneiss plot on a chord intersecting the concordia at 1231 43 and at 975 35 ma the upper intercept age is interpreted as the time of zircon crystallization hence the age of intrusion of the granitic precursor the lower intercept age reflects the time of peak granulite facies metamorphism concordant u pb isotope ratios of a zircon fraction from a charnockite 991 4 ma gives the time of crystallisation of the charnockite garnet whole rock ages sm nd between 911 and 933 ma and biotite whole rock ages rb sr between 866 and 882 ma document the cooling history of the guichicovi complex age and petrography of the guichicovi complex confirm its connection with other granulite exposures in mexico which comprise the oaxaquia microcontinent the results support the hypothesis that the precambrian crust in mexico together with the colombian andes and the adirondacks originated during the mid proterozoic the grenville orogenic event depressed these terranes into the roots of the orogen our data indicate that the guichicovi complex stayed for 70 ma at a deep crustal level before uplift subsequent breakup of rodinia left oaxaquia including the guichicovi complex together with gondwana further collisions of gondwana and laurentia and repeated transpressional interactions in the paleozoic and early mesozoic led to the present day position of grenville fragments in mexico

comparison of the tectonics and geophysics of the major structural belts between the northern and southern continental margins of the south china sea abstract a comparison of the tectonics and geophysics of the major structural belts of the northern and the southern continental margins of south china sea has been made on the basis of measured geophysical data obtained by ourselves over a period of 8 years 1984 1991 this confirmed that the northern margin is a divergent one and the southern margin is characterized by clearly convergent features the main extensional structures of the northern margin are from north to south 1 1 the littoral fault belt a tectonic boundary between the continental crust and a transitional zone along the coast of the provinces of guangdong and fujian in south china it is characterised by earthquake activities high magnetic anomalies and a rapid change in crustal thickness 2 2 the northern and southern depression zones i e the pearl river mouth basin this strikes ne ene and is a very large cenozoic depression which extends from offshore shantou westwards to hainan island 3 3 the central uplift zone this includes the dongsha uplift shenhu uplift and may be linked with the penghu uplift and taiwan shoals to the east forming a large ne striking uplift zone along the northern continental slope it is characterized by high magnetic anomalies 4 4 southern boundary fault belt of the transitional crust this has positive gravity anomalies on the land side and negative ones on the sea side 5 5 the magnetic quiet zone this is located south of the southern boundary fault belt and between the continental margin and the central basin of the south china sea magnetic anomalies in this belt are of small amplitude and low gradient we consider the magnetic quiet zone to be a very important tectonic zone the major structures of southern continental margin southwards are 1 1 the northern fault belt of the nansha block this extends along the continental slope north of the liyue shoal reed bank and zhongye reef and is a tectonic boundary between oceanic crust and the nansha block continental crust 2 2 the nansha block uplift zone due to the development of reefs and shoals there are many channels and valleys our long distance multichannel seismic profiles indicated that there are thick paleogene sediments and thin neogene sediments all over the central part of the block 3 3 the nansha trough a nappe structure formed by the southeastward drifting of nansha block and northwestward overthrusting of palawan northwest borneo 4 4 zengmu shoal basin southwest of the nansha block the maximum thickness of cenozoic strata is over 9 km in this important petroliferous basin

spatial bias in b value of the frequency magnitude relation for the hong kong region abstract the onshore and offshore regions in south guangdong around hong kong exhibit different b values of the g r relation the two regions have yielded b values of 0 85 and 0 67 respectively based on the most complete seismic database for the period 1970 1995 tests on the completeness of the seismic catalogue and dominance of local source zones suggest a fundamentally complete record for m 3 events and the spatial bias in the b values cannot be explained entirely in terms of these two factors the subcatalogue of onshore events with focal depth 6 km has yielded an essentially identical b value as that for the offshore region thus revealing a weak upper crust with diffused seismicity overlying a relatively strong lower crust the present study shows that spatial bias in the b value can be resolved by a proper analysis of the seismic data the interpretation is also consistent with the model that the relative motion between south china and the south china sea is diffused over a broad fault zone along the coast with a higher b value in the upper crust and the lack of a single wrench fault

late mesozoic tectonic structure and evolution along the present day northeastern south china sea continental margin abstract the northeastern south china sea continental margin holds the key to understanding late mesozoic tectonics and evaluating hydrocarbon potentials in mesozoic tectonic and stratigraphic structures offshore southeast china with newly obtained and processed seismic data and new drilling and logging data we correlate regional mesozoic stratigraphy and analyze major mesozoic tectonic events and structures in particular we focus our study on the three major tectonic units in the area the chaoshan depression the tainan basin and the dongsha penghu uplift which are separated by basement high thrust fold and or faults stratigraphic correlations suggest a major phase of southeastward regression spanning in time from the late early jurassic 180 ma to the early cretaceous 120 ma seismic data reveal two major tectonic events with the first one in the late jurassic to the early cretaceous contemporary with the regression and the second one in the late cretaceous regional magnetic anomaly map after the reduction to the pole clearly reveals the boundary between the dongsha penghu uplift and the chaoshan tainan depositional system the seismic and magnetic data also suggest that while the dongsha penghu uplift has highly magnetized sources buried mostly in the upper crust at depths from about 2 km to about 20 km the chaoshan tainan depositional system has thick mesozoic sediments of low magnetization

structural styles of an accretionary wedge south of the island of sumba indonesia revealed by seamarc ii side scan sonar the accretionary wedge south of sumba island indonesia is in the early stages of continent island arc collision australian continental shelf sediments are being actively accreted to the sunda arc at the timor trough we have correlated seamarc ii side scan images and bathymetry with 3 5 khz and seismic reflection profiles to construct a structural interpretation of this zone deformation is concentrated on the lower slope of the accretionary wedge within 15 to 25 km of the thrust front above which the strain rate appears to decrease abruptly three distinct structural styles are developed in the survey area the characteristics of the easternmost region are 1 deformation in a fold and thrust geometry 2 presence of mud volcanoes and mud ridges parallel to the thrust front indicating elevated fluid pressure and 3 the development of a long decollement extending 10 to 15 km from the thrust front in contrast the central region shows a more homogeneous thickening resulting mainly from closely spaced faulting seaward verging thrust faults and conjugate strike slip faults are the main structures in this segment of the accretionary wedge mud volcanoes and a very long decollement are absent in the central region we present a hypothesis in which structural style is controlled by the length of the decollement developed in front of the thrust front short thick thrust sheets may favor uniform shortening whereas long thin sheets may be unstable to buckling and deform by folding high fluid pressure may facilitate propagation of the decollement in contrast to the accretion occurring in the other two regions the western part of the accretionary wedge is in the process of being indented and redeformed by a basement ridge

a grenvillian arc on the margin of amazonia evidence from the southern oaxacan complex southern mexico abstract the rocks in the southern oaxacan complex of mexico form part of the basement of oaxaquia a terrane that underlies most of eastern mexico they have undergone granulite facies metamorphism at 1 ga that was initially overprinted by lower amphibolite facies metamorphism accompanied by extensive hydration and then by greenschist facies metamorphism geochemical data indicate that protoliths include volcanic arc lavas and sediments intruded by a rift related granite the metavolcanic rocks have sio2 ranging between 55 and 72 are typically enriched in highly incompatible elements such as ba rb and light rare earth elements and are accompanied by relative depletion of nb and ti characteristic of subduction related magmas the granite has sio2 ranging between 67 and 70 is enriched in strongly incompatible elements and depleted in nb and ti indicative of either a crustal source or a subduction related tectonic setting concordant u pb analyses of single zircons from this granite yield an age of 1117 4 and 988 5 ma interpreted as the age of intrusion and the time of peak granulite facies metamorphism respectively combined with published information from other parts of mexico these data indicate that oaxaquia was a juvenile arc metamorphosed during a relatively young grenvillian metamorphism at 990 ma similar characteristics may also be found in the andean massifs of colombia and in the appalachian terranes carolina piedmont and avalon of amazonian provenance this suggests that oaxaquia may also have lain adjacent to northwestern amazonia at 1 ga a location that may allow neoproterozoic subduction as the origin of the hydrous lower amphibolite facies metamorphism it would also provide a proximal source for low grade to unmetamorphosed 1 ga and neoproterozoic igneous boulders in northern oaxaquia and 1000 900 ma detrital zircons in neoproterozoic and paleozoic sedimentary rocks in avalonia and iberia

the temporal and spatial distribution of volcanism in the south china sea region cenozoic magmatism in the south china sea the associated continental margins coastal south china and indochina is reviewed volcanism contemporaneous with rifting and sea floor spreading in the south china sea was very weak in the margins and adjacent areas there was only very limited magmatic activity most probably after the cessation of sea floor spreading the south china sea has non volcanic margins large basement relief caused by extension formed major basins and a continental oceanic transitional zone in the northern margin reflects high crustal rigidity during rifting and drifting the paucity of a magma supply and presence of rigid fault blocks are unfavorable to the mantle flow model previously proposed to account for the opening of the south china sea which was supposedly linked to the escape of indochina induced by indo eurasia collision c 2005 published by elsevier ltd

neogene basin history and paleomagnetism of a rifted and inverted forearc region on and offshore sumba eastern indonesia the island of sumba is located in the arc trench gap at the junction of the sunda and banda arcs to elucidate its enigmatic forearc position stratigraphic and paleomagnetic data were collected along three transects in central and east sumba sumba represents the emerged part of a terrane of se asian origin results of stratigraphic and paleomagnetic investigations on central and east sumba are presented and discussed in order to identify patterns of horizontal and vertical crustal movements a synthetic seismogram of the onshore record enables correlation with the offshore neogene e of sumba in order to interpret the data in a regional context the neogene basin history of sumba started when overall subsidence took place around the transition from early to middle miocene on east sumba above a basal condensed interval up to 600 m of middle late miocene volcaniclastic submarine fan deposits occur the sediments reflect island arc volcanism and are interpreted as parts of a prograding submarine fan system on a north dipping paleoslope fed by a volcanic source to the south of sumba biostratigraphic data indicate a high volcanic supply during the middle miocene and early middle tortonian a waning supply during the late tortonian and renewed supply during the messinian these patterns probably reflect variation in volcanic activity during the messinian calcilutites and foraminiferal chalks became dominant and deposition of these pelagic sediments continued into the early pliocene using the pattern of magnetic polarity changes in a selected interval the position of the mioceneepliocene boundary is better constrained seismic studies in the offshore area e of sumba van der werff 1995a b indicate the presence of an extensive tract of n prograding turbidites on sumba ridge savu basin the proposed correlation with the onshore record suggests lateral continuity from the island into the offshore area where the volcaniclastic submarine fan system presumably had its largest development subsidence proceeded so fast i m ka on east sumba that before the beginning of the late miocene sediments were deposited below the ccd this pattern suggests that the sumba region underwent strong crustal attenuation due to rifting as this was coupled with the arrival of volcaniclastics we envisage intra arc rifting coupled with the growth of a short lived volcanic arc further south its initiation at the transition of middle late miocene suggests interaction with the then approaching banda arc subduction system the paleomagnetic data indicate that during this process sumba was at a paleolatitude of 12 south and underwent a counter clockw ise rotation of 5 the reappearance of planktonic foraminiferal assemblages during the latest miocene and their present elevation above sea level suggest an average rate of post miocene uplift of 0 7 mm a emergence of sumba probably did not take place before 3 ma this inverted motion of the sumba terrane is probably coupled with the change to the present tectonic situation in which volcanic activity was resumed in the present inner arc after a non volcanic interval during the spreading stage 1 1997 elsevier science ltd

thrust tectonics along the north western continental margin of sabah borneo widely accepted plate tectonic models suggest that an inactive subduction zone lies along the north west continental margin of sabah in contrast interpretation of reflection seismic data acquired by bgr shows an autochthonous continental terrane comprising an oligocene to early miocene carbonate platform being progressively overthrust by an allochthonous rock complex progressive compression resulted in the development of four structural zones imbricated thrust sheets zone iii two thrust sheet systems one on top of the other zone iv a complex zone with multiphase deformation zone v and piercement ridges zone vi

collisional melange development geologic associations of active melange forming processes with exhumed melange facies in the western banda orogen indonesia analysis of block assemblages matrix clay mineral composition and microfauna and offshore seismic reflection profiles reveal that the bobonaro melange in the timor region is sourced from mud rich australian continental margin sequences that are remobilized during accretion and form various facies depending on the structural conditions of emplacement melange facies include broken formation matrix rich mud injections and classic mixed block in clay facies each of these are distinguished by varying degrees of remobilization mixing and dispersion at different structural positions across the orogenic wedge the most important structural control is whether melange was generated beneath or in front of upper plate banda forearc basement banda terrane at the present collisional deformation front in the timor trough seismic reflection profiles show that melange forms mostly by stratal detachment and fluid assisted remobilization above a basal decollement propagating laterally along overpressured jurassic to cretaceous clay rich sequences of the distal australian continental margin the broken clay rich material injects upward through faults to form intrusive bodies at the base of slope cover sediment to form mud ridges at the surface similar patterns of stratal disruption are exposed onshore in the pliocene kolbano fold and thrust wedge of southern timor which is structurally contiguous with the timor trough deformation front melange in the kolbano mountains is mostly broken formation and matrix rich injections of mud from jurassic and cretaceous units deformation mechanisms include intense layer parallel extension associated with emplacement by mud diapirs that rise from near the decollement upward to the surface along fault conduits in the hinterland of the orogenic wedge east timor and northern west timor melange is dominantly of mixed block in clay facies with large blocks derived from roof thrust sheets of intermixed banda terrane and maubisse formation units at the structural base of these thrust sheets is the sonnebait disruption zone sdz which formed the initial suture between the banda terrane and structurally underthrust australian continental margin sequences during the late miocene to early pliocene the thickest accumulations of mixed block in clay melange in the timor region are found at the southern edge outlet of the sdz near the central and viqueque synorogenic basins the extent of block dispersion and mixing in the sdz is indicative of intense shear strains perhaps induced by an oversupply of accretable material when the suture zone was clogged by underthrusting of the australian continental margin

finite extension across the south vietnam basins from 3d gravimetric modelling relation to south china sea kinematics abstract we derive a crustal thickness map over the south vietnam basins from a 3d inversion of gravity data that takes into account the sedimentary infill and its density variation with depth this map is used to estimate the total amount of stretching across these basins that varies from 190 km to the east at 111 e to 30 km to the west at 107 e comparison with south china sea kinematics amount and timing of oceanic opening implies large decoupling with respect to the indochina block and supports the hypothesis of formation of the south china sea in upper oligocene to lower miocene by southward subduction of the proto south china sea

mesozoic and cainozoic rocks dredged from the south china sea reed bank area and sulu sea and their significance for plate tectonic reconstructions abstract outcrops of pre quaternary rocks were sampled by dredging and coring during two cruises of rv sonne in the south china sea and sulu sea 1982 1983 late triassic deltaic sandstones wih plant remains are the oldest sediments recovered late jurassic early cretaceous regional metamorphism is indicated by gneiss and garnet mica schists exposed in the northwestern flanks of reed bank these rocks and occurrences of gabbro diorite dacite rhyolite and siliceous shale prove that the dangerous grounds and reed bank are underlain by a continental fragment during the period of seafloor spreading in the south china see a late oligocene to early miocene carbonate platform developed on this southwards drifting continental fragment which subsided in the middle miocene middle miocene andesite and early to middle miocene reefal carbonates were recovered from the cagayan ridge in the sulu sea the new data are in accord with the plate tectonic history developed by taylor and hayes 1980 1983 and holloway 1981

stratigraphic succession of the australian margin between kai and aru islands arafura sea eastern indonesia interpreted from banda sea ii cruise dredge samples abstract a fairly complete sedimentary succession 3000 4000 m thick off the australian margin east of kai besar island arafura sea is documented from micropalaeontological analysis of samples from eight dredges collected during the banda sea ii cruise on board baruna jaya iii sediments indicate shelf environment with siliciclastic probably late carboniferous early permian sediments jurassic cretaceous black shales open marine pelagic sediments from late albian to mid late eocene age and shallow water platform carbonate deposited during early miocene from late miocene to holocene times pelagic sediments were deposited because samples were dredged stratigraphic gaps in the succession can only be inferred but the general sedimentary sequence is similar to that of surrounding areas in the arafura sea as known from exploratory wells

deformation and metamorphism of the aileu formation north coast east timor and its tectonic significance abstract the large block of metamorphic rocks along the north coast of east timor is of special interest as it occurs at the boundary between continental and oceanic crust in an island arc continent collision zone a detailed study of the structure and metamorphic history of 400 km2 of this formation showed it has a complex history of penetrative deformation but the structure is coherent pelites psammites and limestones interlayered with dolerites and amphibolites have been metamorphosed in a medium pressure environment they now form a metamorphic province zoned from low greenschist facies in the southwest to upper amphibolite facies in the east the earliest recognised deformation phase predated the metamorphism and produced a widespread layer parallel schistosity but no recognisable folds the second deformation phase post dated the metamorphic maximum and micropetrological evidence indicates a gradual cooling during this event this deformation produced tight folds with an axial plane schistosity and transposed the earlier structures the progressively weaker third and fourth phases developed crenulation cleavages and related folds under greenschist facies conditions open fifth phase macroscopic folds were probably synchronous with strike slip faulting parallel to the north coast later dip slip faulting juxtaposed the aileu formation with permian and mesozoic sediments of very low metamorphic grade reconnaissance k ar radiometric dating using hornblende and biotite showed the prograde metamorphic maximum occurred before 11 ma ago and implies that the second and strongest deformation phase occurred in the late miocene this young age establishes the relationship of the deformation events to the collision between australia and the inner banda arc the proposed models for the structure of timor must be modified to fit the deformation history of the aileu formation if timor is essentially autochthonous the aileu formation was probably deposited in a palaeozoic graben and the metamorphic maximum may have occurred in the jurassic the overthrusting models must be modified in the light of the close correlation in time between penetrative deformation and emplacement of the proposed thrust sheets the analogy proposed between timor and normal convergent margins is not supported but it may be possible to draw analogies with the molucca sea

3d topography of the moho discontinuity in the taiwan area as extracted from travel time inversion of pmp phases abstract the reflective signals are often used to find a particular reflective interface therefore we used the travel time of the pmp phase to investigate the moho depth beneath taiwan in this study we used the directionality and rectilinearity functions to increase the accuracy and the convenience of the pmp phase identification in all we selected 1054 earthquakes with 13 715 travel time data of the pmp phase to invert the attitude of the moho discontinuity from the results we offer these conclusions 1 the distribution of the moho depth in taiwan trends nne ssw which is consistent with the topography 2 the deepest part of the moho discontinuity is beneath the central mountain range 38 km in depth and the depth of the moho discontinuity beneath the peikang basement high is only 26 km 3 the western coastal plain is divided into an active continental margin and a passive continental margin by the peikang basement high 4 the moho depth beneath the northern part of the coastal range is deeper than the southern part because of more vigorous collision activity

revitalising exploration and re development of deep carbonate targets in the southern apennines thrust belt southern italy reappraising vintage data with modern approaches

the structural evolution of the timor collision complex eastern indonesia abstract the structural style of timor is consistent with foreland fold belt processes and zones of frontal accretion and underplating can be recognized in the australian parautochthonous sequence the parautochthon is overlain by an allochthonous sequence which corresponds to the pre collisional oceanic forearc in northern timor the parautochthon has been underplated directly beneath the allochthonous basement unlike previous interpretations of timor in terms of foreland fold belt processes the timor foldbelt is here interpreted as having evolved in a fairly straightforward way from the pre collisional forearc by the sequential addition of thrust slices of australian continental crust to the front and base of the developing collision complex

structural evolution from paleogene extension to latest miocene recent arc continent collision offshore taiwan comparison with on land geology marine structures observed in seismic profiles across the ne south china sea taiwan strait luzon arc region show that they are comparable to those observed onshore taiwan the hanjiang depression and dongsha uplift off the se china coast extend to the penghu basin and penghu platform respectively in the taiwan strait while the tainan basin in the south of penghu platform is connected to the chaoshan depression south of the dongsha uplift the hanjiang depression and the penghu basin are composed of paleogene syn rift sequences on the mesozoic basement and are uncomformably overlain by neogene post rift strata similar successions are found underneath the coastal plain or have been thrust up as a fold and thrust belt bordering the peikang basement high onshore central taiwan east of the manila trench off southwestern taiwan parts of the tainan basin are thrust into the submarine syn collision accretionary wedge the fold and thrust kaoping slope in the initial arc continent collision zone they have also been exposed in the fold and thrust western foothills south of the peikang basement high in southern taiwan during an advanced stage of arc continent collision since the late pliocene further east the pre collision accretionary wedge the hengchun ridge shoals northward to the hengchun peninsula with late miocene turbidites unconformably overlain by plio pleistocene shallow marine slope basin sequences in the arc domain cast of the arc prism boundary fault the western forearc sequences in the north luzon trough are deformed two normal faulted intra arc basins occur on the eastern part of the lanhsu island in the luzon arc the scenario of the deformed forearc sequences and the development of the two intraarc basins in the initial arc continent collision zone are analogous to the lichi melange taiyuan basin and the intra arc basins in the southern coastal range eastern taiwan additionally the lateral change in the marine structure from the passive asian continental margin to the manila subduction system is comparable to the temporal evolution from paleogene normal faulting through neogene subduction to latest miocene recent are continent collision observed onshore taiwan c 2001 elsevier science ltd all rights reserved

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

geologic evolution of the xolapa complex southern mexico evidence from u pb zircon geochronology the xolapa complex of southern mexico is composed of mid crustal arc related gneisses of poorly resolved ages intruded by undeformed cenozoic calc alkaline plutons twelve undeformed and deformed tonalitic granodioritic samples from three transects across the sierra madre del sur acapulco puerto escondido and puerto angel were chosen for u pb zircon analysis the measurements were performed on single crystals of zircons using a multiple collector laserablation inductively coupled plasma mass spectrometer mc la icp ms about 20 30 crystals were measured from each sample three gneisses and migmatites from the eastern transect puerto angel located 30 42 km from the coast yielded grenvilleaged zircons 970 1280 ma suggesting that the samples represent oaxacan basement not deformed xolapa complex the central transect puerto escondido yielded oligocene ages 25 32 ma on undeformed plutons as well as mid mesozoic and permian ages on gneisses most samples along the puerto escondido transect contain inherited ca 1 1 ga xenocrystals of zircons the western transect acapulco yielded late jurassic early cretaceous ages 160 136 ma on gneisses and paleocene 55 ma and oligocene 34 ma ages on undeformed plutons with no inherited grenville ages the older ages and xenocrystic zircons in arc related xolapa complex mirror the crustal ages found in neighboring terranes mixteca and oaxaca to the north of the xolapa complex suggesting an autochthonous origin of xolapa with respect to its neighboring northbounding terranes the new data and previously published ages for xolapa suggest that metamorphism and migmatization of the deformed arc rocks took place prior to the cenozoic eocene and oligocene plutons representing renewed arc related magmatism in the area are common throughout xolapa and probably represent the more deeply exposed continuation of the sierra madre occidental arc to the northwest the available u pb data argue against the previously proposed eastward migration of magmatism between acapulco and puerto angel during the oligocene

u pb geochronology geochemistry and provenance of the grenvillian huiznopala gneiss of eastern mexico abstract the huiznopala gneiss is the smallest 25 km2 of four exposures of grenvillian granulites in eastern and southern mexico the gneiss comprises three major lithologic units 1 a main series of orthogneisses 2 an anorthosite gabbro complex and 3 a layered paragneiss sequence thirty one u pb zircon ages from seven samples all lie within a restricted range of 200 million years and the geochronological results are interpreted to reflect principally a two stage history the earliest stage was arc magmatism that extended from 1200 to 1150 ma the second stage included granulite facies metamorphism which peaked at about 725 50 c and 7 2 1 0 kbar and perhaps emplacement of the anorthosite gabbro complex at 1000 ma a pegmatite with an age of 988 3 ma post dates ductile deformation the timing of ductile deformation and granulite facies metamorphism of the huiznopala gneiss corresponds closely to that of final thrusting and deformation in the grenville province thus the huiznopala gneiss may be in the core of the orogen formed during the final thrusting event recognized in the grenville orogeny gondwanan faunal assemblages are found in lower paleozoic sedimentary rocks that overlie grenvillian granulites elsewhere in mexico however the pb isotope compositions of samples from the huiznopala gneiss overlap with those of the basement from laurentia adirondack highlands and lowlands texas and they are distinct from those of the gondwanan arequipa antofalla craton of southern bolivia and northern chile the magmas parental to the huiznopala arc and those parental to the laurentian crust may have shared a common isotope reservoir and the pb isotope compositions are consistent with the paleomagnetic results that place southern mexico adjacent to ontario quebec at about 950 ma

geochemistry of crude oils from eastern indonesia high resolution geochemistry shows genetic relationships among 27 crude oils from eastern indonesia and suggests the ages and paleoenvironments of their source rocks oils inferred to originate from tertiary and triassic jurassic source rocks in the study occur north and south of 2is latitude respectively twenty oils mainly from irian jaya and sulawesi originated from tertiary marine marlstone source rocks that contained type ii iii kerogen deposited under suboxic conditions probably the upper miocene klasafet formation these low sulfur oils show high oleanane c26 24 nordia cholestane and pristane phytane ratios and 13c rich carbon isotope compositions high oleanane and 24 nordiacholestane ratios are diagnostic of tertiary oils and source rocks these oils account for about 16 of the estimated ultimate recoverable reserves in eastern indonesia

geology of the kai islands implications for the evolution of the aru trough and weber basin banda arc indonesia abstract the kai archipelago is situated at the apex of the 180 bend in the banda island arc topographically the islands occupy a forearc position between the aru trough to the east and the weber forearc basin to the west however the structural style of the eastern kai islands is very different from the rest of the banda forearc being dominated by normal faults downthrowing to the aru trough with no sign of earlier compressive forearc deformation the aru trough is an extensional feature although it is in direct bathymetric continuity with the compressional timor tanimbar trough to the south the banda arc thrust front does not continue simply northward from the timor tanimbar trough but steps westward as a result of extension in the aru trough the thrust front runs n s through the kai group separating an inactive accretionary complex to the west from active extension in the east the weber basin results from e w extension with pre existing thrust faults probably reactivated in extension as low angle normal faults both the compressional and extensional deformation phases have occurred since the pliocene a period of less than 5 my

permo triassic evolution of gondwanan eastern indonesia and the final mesozoic separation of se asia from australia abstract continental fragments with australian gondwanan stratigraphic affinities are widely distributed throughout the eastern indonesia collision complex despite their structural isolation from one another as a consequence of tertiary orogenesis these fragments show a remarkably uniform pattern of permo triassic tectonostratigraphy ranging from a granitoid belt in the north through a continental platform to an intracontinental rift system in the south within the rift system complementary upper and lower plate rifted margins can be recognised in the northern and southern banda arcs respectively the northern granitoid belt was initiated in the mid carboniferous whilst the intracontinental rift system began to develop in latest carboniferous earliest permian times extension in the northern rift margin ceased in the mid carnian early late triassic contemporaneous with a marked decline in igneous activity in the granitoid belt to the north the sibumasu terrane of mainland se asia probably originated on the gondwanaland continental margin adjacent to reconstructed eastern indonesia but rifted away during the early permian previous interpretations have seen this rifting as marking the final separation between gondwanaland and continental terranes now forming se asia alternatively it is suggested here that gondwanan eastern indonesia acted as an indirect continental connection between sibumasu indochina and australia during the permian and triassic this continental isthmus permitted continuing limited floral and faunal interchange between gondwanaland and se asia until a final separation in the late triassic the mid carnian structural event in eastern indonesia is interpreted as related to this separation

neogene block tectonics of eastern turkey and northern south america continental applications of the finite difference method continental plate boundary zones are generally wide diffuse zones of deformation within which in the upper 5 to 15 km may be recognized blocks which are bounded by fault zones within which strain is highly concentrated and along which slip rates are fairly high 2 30 m ma 1 these blocks may be irregular flakes defined by older crustal inhomogeneities of an upper brittle crust below which strain occurs in a ductile and more homogeneous lower crust with examples from the convergent plate boundary zone of eastern turkey and the southern caribbean plate boundary zone of northern south america we use plate slip rates and trends and slip rates of faults to construct block vector diagrams to deduce the sums of relative motion among block mosaics slip rates and trends of ill defined block boundaries and the extent to which blocks are internally strained

thermal and rheological structures of the xisha trough south china sea the xisha trough located in the northwest of the south china sea scs mainly rifted 30 ma ago has been a failed rift since the cessation of the seafloor spreading of the nw subbasin based on the velocity depth model along profile obh 4 across the xisha trough a seven layer density depth model is used to estimate density structure for the profile the relationship between seismic velocity and radiogenic heat production is used to estimate the vertical distribution of heat sources in the lower crust the 2 d temperature field is calculated by applying a 2 d numerical solution of the heat conduction equation and the thermal lithosphere thickness is obtained from the basalt dry solidus bds the rheology of the profile is estimated on the basis of frictional failure in the brittle regime and power law steady state creep in the ductile regime rheological model is constructed for a three layer model involving a granitic upper crust a quartz diorite lower crust and an olivine upper mantle gravity modeling supports basically the velocity depth model the moho along profile obh 4 is of relatively high heat flow ranging from 46 to 60 mw m 2 and the moho beat flow is higher in the trough than on the flanks the depth of the thermal lithospheric lower boundary is about 54 km in the center deepens toward two sides and is about 75 km at the northern slope area and about 70 kin at the southern xisha zhongsha block rheological calculation indicates that the two thinnest ductile layers in the crust and the thickest brittle layer in the uppermost mantle lie in the central region showing that the xisha trough has been rheologically strengthened which are mainly due to later thermal relaxation in addition the strengthening in rheology during rifting was not the main factor in hampering the breakup of the xisha trough c 2002 elsevier science b v all rights reserved

characteristics of surface heat flow in the south china sea a total of 592 heat flow measurements ranging from 8 to 192 mw m 2 78 percent of which are between 50 and 100 mw m 2 have been collected in the south china sea scs to overcome shortcomings such as the uneven distribution of the measurements and the occurrence of abnormal heat flow values the tectonic evolution of different areas and their crustal thickness have been combined in analyzing geothermal characters the results show that the oceanic basins where they are floored by oceanic crust the western part of the southern margin and the western fault system have high heat flow values heat flow along the northern margin of the scs increases from 61 mw m 2 on the shelf to 73 80 mw m 2 in the slope area and in the xisha zhongsha area increases from about 70 mw m 2 to about 85 mw m 2 from the nw to the se heat flow in the nansha spratley islands is about 60 mw m 2 or even higher and decreases from the nw to se the average heat flow of the mekong basin is about 60 mw m 2 which is similar to that of the beibuwan basin on the northern margin heat flow on the eastern margin and on the eastern part of the southern margin is lower especially in the luzon trough where the average heat flow is lower than 40 mw m 2 observed heat flow values in the sw subbasin are generally lower than predicted theoretically from the age of the ocean floor unlike values in the eastern subbasin a high heat flow zone in the lower slope area of the northern margin is recognized for the first time c 2003 elsevier ltd all rights reserved

crustal structure and variation in the southwest continental margin of the south china sea evidence from a wide angle seismic profile abstract a 680 km long wide angle seismic profile was acquired in the southwest continental margin swcm of the south china sea to better understand its crustal variation and continental extension by using two dimensional forward ray tracing and joint refraction and reflection travel time inversion methods velocity structures of the swcm are yielded the model results show a hyper stretched continental crust with a thickness of 10 18 km which is variable under sedimentary basins and reef areas compared with wc uc and lc derived from the crustal thickness the degree of the whole crust extension appears to be larger than that of the upper crust but lower than that of the lower crust except for the model of 560 610 km thus we infer that depth dependent extension of the crust has occurred in the swcm high velocity bodies with velocities larger than 7 0 km s are sporadically distributed in the lower crust which might be related to the remnant mesozoic arc that can be attributed to the subduction of the paleo pacific plate the obvious low velocity anomaly with the maximum thinning crust below the boundaries of the nansha trough and palawan borneo thrust wedge pbtw is interpreted as the frontal thrust of the pbtw

rates of neogene and quaternary tectonic movements in the southern banda arc based on micropalaeontology it is generally considered that the outer banda arc islands are composed in part of strongly deformed sediments that accumulated at the north australian continental margin the onset and completion of folding nappe emplacement imbrication and uplift that produced the islands of the outer banda arc have been dated by means of planktonic foraminifera the dating of the onset of uplift of timor from a deep submarine position at the end of the neogene nappe emplacement to mountains now reaching nearly 3 km high indicates the rate of post collision uplift to have been initially 3 mm yr then it slowed to about 1 5mm yr where the australian continental margin meets the eastern end of the present java trench there are indications that the australian margin has overridden the trench in the timor region by 240 km micropalaeontological dating of the neogene collision between the australian continental slope proximal rise and the trench provides constraints for checking the overriding hypothesis by calculating rates of convergence derived from plate motions 7 5cm yr against the rates based on the tectonic model 7 4cm yr after nappe emplacement possibly faster than 6 25 cm yr shortening of the continental crust appears to have migrated towards the australian continent so that the shelf itself has become involved in the imbrication with shortening of the cover rocks between the nappes and the present shelf edge amounting to about 40 km during the last 2 ma

seismic evidence for central taiwan magnetic low and deep crustal deformation caused by plate collision abstract crustal seismic velocity structure was determined for the northern taiwan using seismic travel time data to investigate the northeastern extension of the northern south china sea s high magnetic belt in order to increase the model resolution a joint analysis of gravity anomaly and seismic travel time data have been conducted a total of 3385 events had been used in the inversion that was collected by the central weather bureau seismological network from 1990 to 2015 the main features of the obtained three dimensional velocity model are 1 a relatively high vp zone with velocity greater than 6 5 km s is observed in the middle to lower crust 2 the high vp zone generally parallels to the north south structural trending of the chuchih fault and hsuehshan range 3 at 25 km depth slice the high vp zone shows structural trends change from northeastward to northward in central taiwan where the values of high magnetic anomalies are rapidly decreasing to low values a combination of seismic gps and structural interpretations suggests that the entire crust has been deformed and demagnetized in consequence of the collision between the philippine sea plate and the asian continental margin we suggest that the feature of sharp bending of the high vp zone would migrate southwestward and cause further crustal deformation of the peikang high in the future

a crustal structure profile across the northern continental margin of the south china sea an ocean bottom seismometer obs geophysical experiment was carried out across the northern continental margin of the south china sea two dimension kinematic ray tracing was used to construct synthetic records and to define the geological model along the obs profile according to the calculation and interpretation of refracted p wave phases the crustal thickness decreases from 22 km obs 1 in littoral area to 8 km obs 15 in deep sea the lower slope structured by volcanism changes sharply in moho depth from 22 to 9 km the volcanoes over the lower slope were markers of ocean continental transition zone a high velocity layer hvl with an average thickness of 4 km was found in the base of the lower crust over the shelf and slope the south china sea was originated by the passive rifting of south china continent and seafloor spreading however geological and geophysical data collected in the northern margin of the south china sea show a small amount of magma intruded into or erupted onto the crust during pull apart and breakup further analysis shows that the hvz in the base of the thinned continental crust was related to magmatism that occurred after the cessation of seafloor spreading of the south china sea magmatism during the crustal extension and breakup is very weak therefore the northern continental margin of the scs is classified as non volcanic passive margin the southern margin of the south china sea has a crust with a steady thickness of 18 24 km which is different from the nor them margin of the south china sea with a gradually thinned crust they constitute an asymmetrically conjugated pair of passive margins c 2001 elsevier science b v all rights reserved

magmatism in the evolution of the south china sea geophysical characterization abstract timing distribution and intensity of magmatism are critical to understanding deep lithospheric processes in the opening of the south china sea scs based primarily on multichannel seismic reflection data and aided with gravity and magnetic anomalies we identify various igneous features such as sills stocks volcanic edifices and volcanoes which are often characterized by high positive seismic amplitudes and or by chaotic or blank reflections beneath them because of their seismic shielding effect we estimate the timing of igneous activities and analyze their areal distribution in the scs region based on seismic stratigraphy we confirm that most igneous emplacements in the scs margins occurred after the cessation of seafloor spreading and are sparse and volumetrically small during the rifting and seafloor spreading phases supporting magma poor margins prior to the breakup of the continental lithosphere by contrast post spreading magmatic activities are widespread in the continental slope areas and in the central scs basin and are most likely triggered by extension in relation to cooling and subsidence of the oceanic and attenuated continental lithosphere which could accumulate a total thermal contractional displacement up to 24 km

paleomagnetism of the middle jurassic summerville formation east central utah the paleomagnetism of the late callovian summerville formation was analyzed to obtain a late middle jurassic paleomagnetic pole for north america a total of 281 samples were collected from 35 sedimentary horizons sites in a single locality in the san rafael swell area of east central utah fifteen site mean characteristic remanent magnetization chrm directions pass the reversals test and define at least five polarity zones within 52 m of stratigraphic section suggesting that the chrm was acquired upon or soon after deposition magnetizations of some specimens are complex and several horizons yield anomalous site mean directions data analysis included filtering to provide different combinations of virtual geomagnetic poles for calculation of the paleomagnetic pole however editing the data did not change the pole position by more than 5 the preferred paleomagnetic pole position is 56 3 n 133 4 e a95 7 2 n 11 sites the summerville formation paleomagnetic pole is located near the 172 ma corral canyon pole and is statistically indistinguishable from the 151 ma glance conglomerate and 149 ma lower morrison poles the paleomagnetic pole from the summerville formation is located at a much lower latitude and more easterly longitude than the paleomagnetic pole obtained from the 165 ma moat volcanics of new england we propose that the jurassic north american apparent polar wander path is an age progressive band at 55 n to 65 n latitude extending from 11 e longitude at 172 ma to 150 e longitude at 149 ma

the sumba enigma is sumba a diapiric fore arc nappe in process of formation abstract the anomalous updomed morphological expression of sumba island its enigmatic lack of strong neogene deformation and the northward morphological indentation of southern sumbawa and flores require explanation the stratigraphy of sumba may be correlated with the cretaceous to miocene part of the timor allochthon the sedimentary and eruptive rock succession in sumba shows remarkable similarities with the allochthonous palelo wiluba and cablac deposits of timor in both islands the cretaceous parts of these sequences are regarded as characteristic of fore arc deposits built on thin continental crust the timor nappe is interpreted as a 5 km thick tectonic flake of the banda fore arc thrust onto the australian continental margin in the mid pliocene collision the postulated sumba nappe has not yet been thrust onto the australian margin which in the sumba region has not yet converged as close to the arc as in the timor area the postulated sumba nappe is interpreted as a diapiric elongated dome of the sunda fore arc that is being squeezed by the converging margin of australia against the volcanic islands of sumbawa and flores the absence of indications on the seismic reflection profiles for the presence of the thrust fault of the sumba nappe may perhaps be explained by the thrusts being nearly horizontal within flat lying strata the savu thrust is correlated with the probably older pre late pliocene wetar suture as a major southward dipping lithospheric rupture east of 124 e this suture does not seem to have moved much since the mid pliocene collision that emplaced the nappes on timor however microearthquake data suggest some activity is continuing

thermo rheological structure of the northern margin of the south china sea structural and geodynamic implications abstract rheological properties of continental lithosphere are key controls on the behavior of continental deformation using thermal structure constrained by surface heat flow data and measured thermal properties of rocks the present study calculates different thermo rheological structure scenarios for the ocean continent transition oct at the northern margin of the south china sea using two different models a conventional model taking into account frictional sliding and power law creep and a model that additionally includes a high pressure brittle fracture mechanism two compositions of the lower part of the lithosphere are considered a soft case with felsic granulite lower crust and wet peridotite lithospheric mantle and a hard case with mafic granulite lower crust and dry peridotite lithospheric mantle the former scenario shows a major rheological change from a jelly sandwich to a christmas tree type of rheology from north to south along the margin this complex rheological structure explains lateral changes in earthquake distribution and geometries of extensional faults of the oct at the northern margin of the south china sea further our analyses indicate that the initial lithospheric rheology profile probably has only one ductile layer in the lower part of upper crust such an initial lithospheric rheology model predicts focused extension to form asymmetric margins which is the case for the scs

paleomagnetism of the chiapas massif southern mexico evidence for rotation of the maya block and implications for the opening of the gulf of mexico we have analyzed 180 oriented samples of the batholithic complex and overlying red beds of the chiapas massif in southern mexico for a paleomagnetic study both stepwise alternating field and thermal demagnetization procedures revealed dual polarity characteristic magnetizations above 10 30 mt or 200 400 c in about 60 of the samples demagnetized three distinct and ancient paleomagnetic directions have been identified late permian intrusions 256 10 ma yield nearly equatorial southern hemisphere paleolatitudes and a paleopole 13 4 s 176 1 e 12 sites k 15 4 a95 11 4 rotated 75 counterclockwise with respect to the north american reference pole a selected set of late triassic jurassic red beds of the todos santos formation yields a paleopole at 22 6 n 170 6 e 4 sites k 56 8 a95 12 3 which implies 60 counterclockwise rotation and a near equatorial northern hemisphere paleolatitude middle late jurassic dikes and granites yield a paleopole at 77 4 n 97 4 e 6 sites k 269 2 a95 4 1 near the mid jurassic segment of the north american apparent polar wander path these data are consistent with a pre rift configuration in which the maya block is rotated to a position off the coast of texas and louisiana in the present day area of the gulf of mexico a further implication is that by oxfordian times chiapas and by inference the maya block was essentially in its current position with respect to cratonic north america

proterozoic geologic evolution of the sw part of the amazonian craton in mato grosso state brazil abstract this paper presents new geochronologic isotopic and geochemical data bearing on the evolution of proterozoic crust in sw mato grosso state brazil which is at the southern end of the 1 6 1 8 ga rio negro juruena orogenic belt of the amazonian craton amazonia our data define three major crustal events i the alto jauru terrane occurs in the eastern part of the region and is comprised of island arc related rocks with u pb ages from 1 79 to 1 74 ga these rocks have e nd t values range from 2 8 to 2 0 with crustal residence ages t dm from 1 93 to 1 78 ga indicating a mainly juvenile signature at 1 8 ga ii the cachoeirinha suite occurs in the central part of the region and consists of calc alkaline plutons emplaced into alto jauru terrane host rocks these plutons have u pb ages from 1 56 to 1 54 ga and e nd t values ranging from 1 0 to 0 8 with crustal residence ages t dm from 1 88 to 1 75 ga we interpret this orogen as the roots of a continental margin arc built upon basement comprised of the alto jauru terrane iii the santa helena batholith occurs in the western part of the region and is a large elongate body of calc alkaline rocks ranging from granodiorite to highly evolved granite these units yield u pb ages from 1 45 ma to 1 42 ga with e nd t values ranging from 4 1 to 2 6 and crustal residence ages t dm from 1 70 to 1 50 ga the rio alegre domain occurs west of the santa helena batholith and includes juvenile 1 52 to 1 47 ga volcanic and mafic plutonic rocks regional geologic relationships suggest that these rocks are part of the crust into which the santa helena batholith was emplaced we interpret this batholith as the magmatic core of a juvenile arc accreted to the edge of the alto jauru terrane with incorporation of some older crust alto jauru terrane in the east and derivation from mainly juvenile crust rio alegre domain in the west the rio branco suite occurs to the east of exposed alto jauru terrane rocks as large hills protruding through younger aquapei group sedimentary rocks it consists of gabbro and granophyric rocks with u pb ages of 1 47 ga gabbro and 1 43 ga granophyre and inherited older nd suggesting hinterland derivation from alto jauru terrane basement during development of the santa helena batholith several undeformed 1 5 1 4 ga granitic plutons occur within the alto jauru terrane these are also regarded as inboard manifestations of subduction related magmatism associated with accretion of the rio alegre domain and formation of the santa helena batholith the siliciclastic aguapei group was deposited sometime between 1 0 and 1 4 ga it overlies jauru terrane basement rocks of the santa helena batholith and the rio alegre domain in the east it is flat lying and undeformed but in the west it is deformed and metamorphosed in the nnw trending aguapei thrust belt farther west the aguapei group is horizontal undeformed and overlies the paleoproterozoic paragua block in bolivia where it has been correlated with the sunsas group the aguapei thrust belt has k ar cooling ages of about 930 ma and is apparently a foreland fold and thrust belt formed by reactivation of an older rift basin during the 1 0 ga sunsas orogeny which occurs west of the paragua block in bolivia

paleozoic evolution of southern margin of permian basin prior to late pennsylvanian time the permian basin of west texas was a part of the southern margin of the north american craton and was the site of shallow warm water carbonate deposition as the south american margin of gondwana gradually moved northwestward during late paleozoic time the oceanic floor deposits and overlying turbidite fan deposits between north america and south america became parts of large accretionary wedges of semiconsolidated sediments in a series of steps these wedges were folded and thrust toward the northwest against then finally onto the southern margin of north america these compressive steps caused the repeated piling up of the accretionary wedges to form rapidly eroding highlands on the cratonic margins repeated loading on the north american margin formed a series of elongate deep water depositional troughs fore deeps immediately north and west of the accretionary wedges and these received thick accumulations of turbidites the youngest of these deep basins include the northwestern part of the val verde basin to the north and the marfa basin to the west which received basinal deposits from within desmoinesian into early late permian time loading of the cratonic margin also resulted in renewed faulting along generally northwest to north trending older zones of weakness these zones are apparently of precambrian age on the craton the late paleozoic faults mainly had high angle to vertical fault planes and commonly had large components of horizontal displacement this fault system outlines the major uplifts and basins in the permian basin region the joining together of gondwana and euramerica across the marathon salient of the orogenic belt was essentially completed by mid wolfcampian time after that time the southern margin of the permian basin represented by the dugout and marathon allochthons and the diablo platform became a relatively stable tectonic area the glass mountains expose a series of north and northwest dipping cuestas of permian carbonate shelf and shelf edge deposits that accumulated on a platform constructed from these two allochthonous accretionary wedges these permian deposits prograded north and northwestward into the narrow hovey channel which connected the marfa basin with the southern end of the delaware basin carbonate reef growth finally restricted the inflow of marine water into the delaware basin near the end of late guadalupian time

impact of lithospheric flexure on the evolution of shallow faults in the timor foreland system abstract re evaluation of structural evolution on the laminaria high timor sea australia shows that lithosphere flexure associated with the tertiary collision between the australian north west margin and the banda volcanic arc is an important mechanism for neogene fault development and the reactivation of jurassic structures 2d elastic models of the lithosphere flexure show that increasing flexural extension is likely to affect the laminaria high from the late miocene onwards the evaluation of the neogene fault slip history based on instantaneous throw estimates suggests an initiation of faulting during the late miocene when the laminaria high entered the flexed area forebulge increasing fault growth is recorded during the pliocene and correlates with the laminaria high reaching the hinge of the forebulge structure maximum episodes of fault growth are recorded between the late pliocene and early pleistocene when the laminaria high was located near the forebulge hinge or in the slope where curvature and flexural stress are likely to be maximal nnw extension associated with plate flexure allowed the oblique extensional reactivation of buried reservoir bounding jurassic structures the orientation of the jurassic structures relative to the flexural extensional front appears as a key factor controlling the type of segment linkage between the reactivated jurassic faults and the newly developed neogene faults observations from the laminaria high suggest that with an angle 20 between hmax and strike orientation of the jurassic faults soft linkage is likely to occur between jurassic and neogene segments an angle

the petroleum potential of inversion anticlines in the banda arc the banda arc in eastern indonesia and newly independent timor leste east timor is the zone of collision between the northern margin of the australian continent and an oceanic island arc system bordering the eurasian plate structurally the banda forearc is a fold and thrust belt consisting of the imbricated outer edge of the australian continent overlain locally by fragments of the precollisional oceanic forearc the banda forearc is an established petroleum province in the island of seram but the remainder of the forearc has so far yielded no further exploration success despite close geological similarity to seram a major disincentive to exploration in the banda forearc has been a common perception of structural complexity this complexity may however have been overstated and this paper presents a simple structural model for the evolution of the banda forearc key to this model is the recognition of basement involved inversion structures in the deeper parts of the collision complex the inverted graben basins are filled with permianjurassic continental margin sequences including high quality source rocks of late triassicearly jurassic age and contemporaneous potential reservoir sequences sealed by middlelate jurassic shales these jurassic shales also act as an important decollement horizon separating shallow level structural complexity from a simpler structural style beneath characterized by large inversion anticlines the oseil field in seram may be located in such an inversion anticline and comparable prospective structures are identified elsewhere in the banda forearc particularly in timor and the tanimbar islands

deepwater fold and thrust belt classification tectonics structure and hydrocarbon prospectivity a review abstract deepwater fold and thrust belts dwftbs are classified into near field stress driven type 1 systems confined to the sedimentary section and type 2 systems deformed by either far field stresses alone or mixed near and far field stresses dwftbs can occur at all stages of the wilson cycle up to early stage continent continent collision type 1 systems have either weak shale or salt detachments they occur predominantly on passive margins but can also be found in convergent related areas such as the mediterranean and n borneo examples include the niger and nile deltas the west coast of africa and the gulf of mexico type 2 systems are subdivided on a tectonic setting basis into continent convergence zones and active margin dwftbs continent convergence zones cover dwftbs developed during continent arc or continent continent collision and those in a deepwater intracontinental setting e g w sulawesi makassar straits active margins include accretionary prisms and transform margins the greatest variability in dwftb structural style occurs between salt and shale detachments and not between tectonic settings changes in fold amplitude and wavelength appear to be more related to thickness of the sedimentary section than to dwftb type in comparison with shale salt detachment dwftbs display a lower critical wedge taper more detachment folds long and episodic duration of deformation and more variation in vergence structures unique to salt include canopies and nappes accretionary prisms also standout from other dwftbs due to their relatively long continuous duration rapid offshore propagation of the thrust front and large amount of shortening in terms of petroleum systems many similar issues affect all dwftbs these include the oceanward decrease in heat flow offshore increase in age of mature source rock and causes of trap failure e g leaky oblique and frontal thrust faults breach of top seal by fluid pipes one major difference between type 1 and type 2 systems is reservoir rock high quality continent derived quartz rich sandstones are generally prevalent in type 1 systems more diagenetically reactive minerals derived from igneous and ophiolitic sources are commonly present in type 2 systems or many are simply poor in well developed turbidite sandstone units however some type 2 systems particularly those adjacent to active orogenic belts are partially sourced by high quality continent derived sandstones e g nw borneo s caspian sea columbus basin in some cases very high rates of deposition in accretionary prisms adjacent to orogenic belts coupled with uplift due to collision results in accretionary prism related fold belts that pass laterally from sub aerial to deepwater conditions e g s caspian sea indo burma ranges the six major hydrocarbon producing regions of dwftbs worldwide gulf of mexico niger delta nw borneo brazil west africa s caspian sea stand out as differing from most other dwftbs in certain fundamental ways particularly the very large volume of sediment deposited in the basins and or the great thickness and extent of salt or overpressured shale sdetachments

seismic structure in the northeastern south china sea s wave velocity and vp vs ratios derived from three component obs data a nearly 500 km long seismic profile with reflective and refractive wide angle ocean bottom seismometer obs data and multi channel seismic mcs data was acquired across the northeastern continental margin of the south china sea scs the s wave crustal structure and vp vs ratios have been obtained based on a previously published p wave model using the software raylnvr modeling of vertical and horizontal component obs data yields information on the seismic crustal velocities lithology and geophysical properties along the obs 2001 seismic profile s wave velocities in the model increase generally with depth but exhibit high spatial variability particularly from the shelf to the upper slope of the northeastern scs margin vp vs ratios also reveal significant lithological heterogeneity dongsha penghu uplift dpu is a tectonic zone with a thicker crust than adjacent areas and a high magnetic anomaly with a vp vs of 1 74 and a p wave velocity of 5 0 5 5 km s the dpu primarily consists of felsic volcanic rocks in the upper crust and is similar to the petrology of zhejiang fujian volcanic provinces which perhaps is associated with a mesozoic volcanic arc the ocean continent transition oct in the northeastern scs is characterized by a thinning continental crust volcanoes in the upper crust and a high velocity layer hvl in the lower crust the s wave velocity and vp vs ratio suggest that the hvl has a mafic composition that may originate from underplating of the igneous rocks beneath the passive rifted crust after the cessation of seafloor spreading c 2009 elsevier b v all rights reserved

the structural setting and tectonic significance of the lolotoi laclubar and aileu metamorphic massifs east timor abstract the lolotoi and laclubar metamorphic massifs of east timor form a part of the lolotoi metamorphic complex based on stratigraphic relationships with the australian affinity parautochthonous stratigraphic succession and structural arguments the lolotoi complex is interpreted as representing australian continental basement entrained into the timor arc continent collision complex by basement involved thrusting the lolotoi complex is not synonymous with the mutis complex defined from west timor which represents allochthonous metamorphic basement derived from the pre collisional banda forearc the aileu complex is a syn collisional metamorphic series with an inverted metamorphic gradient developed beneath overthrust allochthonous peridotite

osl dating of late holocene coastal sediments and its implication for sea level eustacy in hainan island southern china abstract since the sea level rise is not geographically homogeneous but rather shows great regional differences optically simulated luminescence using quartz as a natural dosimeter has proved to be a powerful and reliable dating technique to determine depositional ages of young coastal sediments around the world the samples acquired from one beach ridge and two marine terraces in coastal hainan island southern china are detected osl dating for the investigation of sea level changes the results show 1 coastal sands in hainan island were well bleached before deposition and the quartz osl can date coastal sediments younger than 200 years which could be one of good indicators for paleo relative sea level highstand records 2 three coastal sediments with 4 m 3 7 m and 2 m higher than present sea level were deposited at 2 40 0 05 ka 2 92 0 17 ka and 4 26 0 10 ka respectively which indicate that the height of highstand relative sea level are higher than both mean global sea level eustacy and those records offshore southern china 3 comparisons with tropical cyclones observations around south china sea indicates that the late holocene coastal sediments of hainan island might have been reformed by tropical cyclones with a highstand sea level

new insights into the history and origin of the southern maya block se mexico u pb shrimp zircon geochronology from metamorphic rocks of the chiapas massif the histories of the pre mesozoic landmasses in southern mexico and their connections with laurentia gondwana and among themselves are crucial for the understanding of the late paleozoic assembly of pangea the permian igneous and metamorphic rocks from the chiapas massif as part of the southern maya block mexico were dated by u pb zircon geochronology employing the shrimp sensitive high resolution ion microprobe facility at stanford university the chiapas massif is composed of deformed granitoids and orthogneisses with inliers of metasedimentary rocks shrimp data from an anatectic orthogneiss demonstrate that the chiapas massif was part of a permian 272 ma active continental margin established on the pacific margin of gondwana after the ouachita orogeny latest permian 252 254 ma medium to high grade metamorphism and deformation affected the entire chiapas massif resulting in anatexis and intrusion of syntectonic granitoids this unique orogenic event is interpreted as the result of compression due to flat subduction and accretionary tectonics shrimp data of zircon cores from a metapelite from the ne chiapas massif yielded a single grenvillian source for sediments the majority of the zircon cores from a para amphibolite from the se part of the massif yielded either 1 0 1 2 or 1 4 1 5 ga sources indicating provenance from south american sunsas and rondonian san ignacio provinces

caltepec fault zone an early permian dextral transpressional boundary between the proterozoic oaxacan and paleozoic acatlan complexes southern mexico and regional tectonic implications 1 the tectonic boundary between the grenville age oaxacan and paleozoic acatlan crystalline complexes in southern mexico named the caltepec fault zone cfz is characterized for the first time as a dextral transpressional nnw trending and ene dipping ductile fault zone of early permian age the complexes are welded by a syntectonic magmatic epidote bearing granite along the entire length of the cfz from east to west the 2 6 km wide cfz consists of disrupted and retrograded banded gneisses of the oaxacan complex quartz feldspar mylonite and the syntectonic magmatic epidote bearing cozahuico granite czg with huge xenoliths up to several kilometers long and up to 600 m wide of the proterozoic gneisses thrust westward over metasedimentary tectonites of the acatlan complex the czg shows magmatic fabrics that represent a transition to solid state deformation characterized by subvertical foliation subhorizontal nne and sse dipping mineral stretching lineation and dextral kinematics the megaxenoliths underwent partial melting developing banded migmatites with layers of epidote bearing granitic neosome the parallelism of fabrics in these anatexitic rocks and in the enclosing deformed granite suggests that ductile deformation migmatization of xenolithic gneisses and granite emplacement along the cfz were coeval the neosome yielded a u pb zircon concordant age of 275 6 1 ma probably dating the peak of the tectonothermal event we interpret the cfz as a major terrane boundary accommodating transpressional interaction between the acatlan and oaxaquia blocks which were amalgamated in an oblique convergent setting by early permian time as the leading edge of gondwana impinged onto the southern margin of laurentia along the marathon ouachita suture to form pangea

hot orogens tectonic switching and creation of continental crust many granulite terrains were too hot to have formed during continental collision rather along with many high grade metamorphic terrains that typify continental crust most formed in accretionary orogens during tectonic switching when prolonged lithospheric extension was interrupted by intermittent transient contraction based on modern and ancient examples tectonic switching occurs when slab retreat induces upper plate extension causing arc splitting formation of microcontinent slivers and backarc basins then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction or slab flip and crustal thickening during slab retreat basaltic magmas produced from decompressed asthenosphere advect into the extending orogen causing granulite facies metamorphism and granite generation but subsequent thickening during flat subduction cools the region thickening is focused in the thermally softened backarc region and if sediment filled a hot short lived 10 m y narrow 50 100 km orogenic belt forms such thickening is often misleadingly ascribed to arc or microcontinent collision once slab retreat mode is reestablished lithospheric extension recommences and a new arc backarc system forms generally outboard arrival of another plateau will reverse the procedure and another short lived hot orogen will form within the orogenic system cycles of tectonic switching efficiently produce continental crust

evidence for paleoproterozoic grenvillian and pan african age gondwanan crust beneath northeastern mexico abstract a number of previous studies including two recent reconstructions of rodinia have considered the grenvillian basement of mexico to be continuous with the laurentian basement of texas isotopic studies and u pb dating of zircons from precambrian granitoids that occur as cobbles and boulders in a paleozoic conglomerate exposed in the state of coahuila northeastern mexico indicate the region is underlain by gondwanan rather than laurentian basement essentially nothing was known of the basement before this study because the region is blanketed with phanerozoic sedimentary and volcanic deposits nine out of ten analyzed samples have grenvillian crystallization ages 1232 7 to 1214 2 ma this phase of magmatic activity in northeastern mexico was coeval with the construction of volcanic arcs in east central and southern mexico 1220 1150 ma but was later than the arc magmatism of laurentia e g elzevirian arcs 1230 ma in texas and the grenville province a subset of the grenvillian samples contains xenocrystic 1 85 ga zircons which are the first evidence of paleoproterozoic crust south of the paleozoic ouachita suture in mexico the remaining sample has a pan african crystallization age 580 4 ma and this is the first sample of pan african age basement found in mexico the pan african orogeny marked the assembly of gondwana and laurentia was unaffected by that event two lines of evidence argue that some of the grenvillian rocks of northeastern mexico were affected by a pan african age event first two of the grenvillian clasts have u pb lower intercept ages within error of 580 ma second common pb and nd isotopic compositions of the pan african granite strongly suggest that it was derived either by melting of grenvillian basement or by assimilating massive amounts of that basement thus far no other grenvillian terrane is known to have the exact combination of nd pb isotopic compositions and absolute ages as the coahuila samples although there are some similarities with the santa marta massif of colombia and the cordillera de merida of venezuela

the triassic of timor lithostratigraphy chronostratigraphy and palaeogeography the palaeontologically rich and lithologically diverse triassic successions of timor provide a key stratigraphic and palaeontological link between northwestern australia and other terranes of former eastern gondwana present day southeast asia timor is now located in the zone of collision between the northern margin of the australian continent and island arc terranes bordering the eurasian plate with the triassic successions exposed in a fold and thrust belt and an extensive melange complex three formal lithostratigraphic units have been defined previously within the main triassic succession in timor niof aitutu and babulu formations with a fourth the wai luli formation primarily jurassic in age but extending down into the triassic the niof formation anisian to ladinian possibly also early triassic is a fine grained deepwater succession succeeded conformably by the aitutu and babulu formations ladinian to norian rhaetian which were deposited contemporaneously with the aitutu formation continuing locally into the lower jurassic the aitutu formation consists of deep shelf limestones interbedded with shales and marls while the babulu formation is a deltaic to turbiditic siliciclastic succession the late triassic to jurassic wai luli formation is characterised by marine shales and marls informal stratigraphic units include the cephalopod limestone facies a rosso ammonitico type deposit which contains an extremely rich fossil fauna particularly ammonoids and ranges through the entire triassic and the fatu limestone and pualaca facies which consists of shallow to marginal marine carbonates mud mounds oolitic limestones and reefs restricted to the late triassic facies diversity was low during the early triassic and anisian but became more pronounced from the ladinian and continuing through the late triassic probably as a consequence of renewed tectonic extension triassic extension was not associated with major volcanism unlike a previous phase of extension in the early permian the cablac limestone formation originally defined as a miocene stratigraphic element is now recognised to be at least partly late triassic early jurassic in age with lithologies comparable to parts of the fatu limestone the stratigraphy of these shallow marine carbonate sequences is clearly in need of rigorous revision but it is not yet possible to suggest appropriate redefined formations

isotopic studies of the acatlan complex southern mexico implications for paleozoic north american tectonics the paleozoic acatlan complex and grenville age oaxaca terrane of southern mexico have been suggested to be the southern continuation of north american orogenic systems the oaxaca terrane yields interpreted ages of 1 0 ga and has many of the characteristics typical of grenville belt rocks the paleozoic acatlan complex consists of multiply deformed metasedimentary rocks schists granitoids and eclogites that have been compared to rocks of the appalachian belt the northward extension of both the oaxaca terrane and acatlan complex how ever are obscured by younger rock cover as they enter central mexico furthermore the configuration of these orogenic systems in southern mexico is the reverse of that of the rest of north america with the grenville oaxaca terrane to the east of the paleozoic acatlan complex isotopic studies show that the acatlan complex records three tectonothermal events the sm nd whole rock mineral isochrons from schists as well as eclogites yield metamorphic ages of 410 380 ma this age of metamorphism is supported by u pb zircon data from a granitoid which yields an age of 370 34 ma a later intrusion of a large stock in the late pennsylvanian 287 2 ma was probably closely followed by a less significant deformational event small granitic intrusions and migmatites were later emplaced at 205 170 ma rb sr and sm nd mineral whole rock the metasedimentary rocks and paleozoic granitoids of the acatlan complex have present day e nd of 9 to 11 with crustal residence ages t dm of 1 3 1 6 ga these rocks must have been derived at least in part from a proterozoic source area and it is significant that crustal residence ages are identical to those of the oaxaca terrane the oaxaca terrane along with some south american precambrian complexes of which the oaxaca terrane was probably once a part may be considered the most likely source areas for the acatlan complex the less extensive eclogite trondjhemite and amphibolite bodies in the acatlan complex yield model ages that show them to be juvenile additions to the crust neodymium model ages of the acatlan complex are unlike those of some accreted crustal blocks of the pacific margin such as the alexander stikine and wrangellia terranes which have little signs of crustal recycling similarities between the acatlan complex and the acadian belt as well as current paleozoic paleogeographic and paleomagnetic reconstructions suggest that the devonian metamorphic event that affected these two areas was the result of a laurentia gondwana collision a later collision in late carboniferous time caused deformation in the acatlan complex plutonic activity in southern mexico and deformation in the ouachita marathon and appalachian belts both the acatlan and oaxaca terranes would have been continuous with south america until the break up of pangea in the mesozoic era

isotopic comparison of k t boundary impact glass with melt rock from the chicxulub and manson impact structures the discussion of candidate source craters for the catastrophic impact that occurred at the boundary between the cretaceous and tertiary periods k t boundary has recently centred on two buried craters the chicxulub in mexico 200 km diameter and the manson in iowa 35 km diameter both of which have 40ar 39ar ages of 65 myr indistinguishable from that of impact glass spherules found in k t boundary sediments1 4 here we report the strontium neodymium and oxygen isotopic compositions of core samples of impact melt rock recovered from drill holes into both the chicxulub and manson craters and compare these with previously published isotopic data for impact glasses from the k t boundary of the beloc formation in haiti5 7 the chicxulub melt rocks are isotopically indistinguishable from the k t impact glass strongly supporting the proposition that chicxulub is a source crater for the k t catastrophe the manson melt rocks by contrast have a clearly different isotopic composition strongly suggesting that they are unrelated to the k t impact spherules

990 and 1100 ma grenvillian tectonothermal events in the northern oaxacan complex southern mexico roots of an orogen inliers of f1 0 1 3 ga rocks occur throughout mexico and form the basement of the oaxaquia microcontinent in the northern part of the largest inlier in southern mexico rocks of the oaxacan complex consist of the following structural sequence of units from bottom to top which protolith ages are 1 huitzo unit a 1012f12 ma anorthosite mangerite charnockite granite amcg suite 2 el catro n unit z1350 ma orthogneiss migmatized at 1106f6 ma and 3 el marquez unit z1140 ma para and orthogneisses these rocks were affected by two major tectonothermal events that are dated using u pb isotopic analyses of zircon a the 1106f6 ma olmecan event produced a migmatitic or metamorphic differentiation banding folded by isoclinal folds and b the 1004 978f3 ma zapotecan event produced at least two sets of structures z1 recumbent isoclinal class 1c 3 folds with gently nw plunging fold axes that are parallel to mineral and stretched quartz lineations under granulite facies metamorphism and z2 tight upright subhorizontal wnw to nne trending folds accompanied by development of brown hornblende at upper amphibolite facies metamorphic conditions cooling through 500 jc at 977f12 ma is documented by 40 ar 39 ar analyses of hornblende fold mechanisms operating in the northern oaxacan complex under zapotecan granulite facies metamorphism include flexural and tangential longitudinal strain accompanied by intense flattening and stretching parallel to the fold axes subsequent phanerozoic deformation includes thrusting and upright folding under lower grade metamorphic conditions the zapotecan event is widespread throughout oaxaquia and took crustal rocks to a depth of f25 30 km by orogenic crustal thickening and is here designated as zapotecan orogeny modern analogues for zapotecan granulite facies metamorphism and deformation occur in middle to lower crustal portion of subduction and collisional orogens contemporaneous tectonothermal events took place throughout oaxaquia and in various parts of the genvillian orogen in laurentia and amazonia d 2003 elsevier science b v all rights reserved