diagnostic features and field criteria in recognition of tectonic sedimentary and diapiric melanges in orogenic belts and exhumed subduction accretion complexes abstract multiple episodes of deformation during the tectonic evolution of orogenic belts and ancient subduction accretion complexes cause obfuscation of primary block in matrix fabric of melanges and thereby making the recognition of their tectonic sedimentary or diapiric origin difficult here we present a comprehensive overview and synthesis of a diverse set of field based stratigraphic and structural criteria which are at the base of geological mapping rules to differentiate between various melange types developed by disparate geological processes and mechanisms we first define the current concepts of melange and melange nomenclature and describe the most diagnostic features of tectonic sedimentary and diapiric melanges at different scales we discuss some of the main issues complicating the application of these diagnostic criteria such as i similarities between the block in matrix fabric of different melange types formed in partially lithified sediments at shallow structural levels ii transformation of fabric elements with increased depth due to tectonic reworking and recrystallization processes iii significance of exotic versus native blocks in melange matrix and iv age relationships between blocks and matrix in a melange we introduce two additional criteria in approaching these complexities and in recognizing different processes of polygenetic melanges formation in the field when primary diagnostic fabrics were reworked by multiple deformational events these new criteria are based on i the coherence between lithological compositions of melange components blocks and matrix and characteristics and tectonic evolution of the geodynamic setting of their formation tectonic environment criterion and ii specificity and kinematic coherence in the distribution of deformation between blocks and the matrix deformation criterion the discussed diagnostic criteria can be applied to all field based investigations of melanges and broken formations in orogenic belts and exhumed subduction accretion complexes around the world regardless of their location age and tectonic history

deformation and sedimentation along a developing terrane suture eastern sunda forearc indonesia the collision of the eastern sunda arc with northwest australia has resulted in the development of a suture between the sumba ridge and sawu timor terranes along a zone of intraforearc convergence the developing suture varies from the low angle sawu thrust with attendant mud diapirs in the sumba basin to high angle reverse faults near a basement high of the underthrust sumba ridge terrane bottom currents associated with the flow of pacific ocean deep water into the indian ocean have eroded the terranes and subsequently deposited the detritus in an assemblage of contourites along the suture this study reveals the high structural variability of a terrane suture and the oceanographic influence on the deposition of overlap assemblages

surface uplift history of the incipient banda arc continent collision geology and synorogenic foraminifera of rote and savu islands indonesia abstract field mapping and analysis of foraminifera from synorogenic pelagic units of rote and savu islands indonesia reveals high rates of surface uplift of the incipient banda arc continent collision during the past 1 8 myr new geological maps of these islands document accretion to the banda forearc of triassic through tertiary sedimentary cover units from the down going australian continental margin foraminifera rich synorogenic deposits of the batu putih formation unconformably overlie these accreted units we use paleodepth versus time estimates from benthic and planktic foraminifera s to measure long term surface uplift rates for the accretionary wedge although strong currents in the region cause some problems with reworking several distinctive species have been found synorogenic deposits in savu and rote yield foraminifer s of biozone neogene n 18 to n22 5 6 1 0 myr that were deposited at estimated depths of around 3000 m these deposits are unconfomrably overlain by uplifted coral terraces the highest coral terraces in savu are 300 m above sea level and perhaps as old as 0 8 myr in rote the highest coral terrace is 200 above sea level and 0 2 myr old these data indicate that collision of the australian continental margin with the banda arc which initiated much earlier in timor has propagated westward towards rote where it is in the initial stages of accretionary wedge emergence collision of the scott plateau propagated se from sumba 2 3 ma to savu 1 0 0 5 ma and then to rote 0 2 ma average rates of surface uplift of the batu putih formation pelagic deposits during the past 2 myr in rote and savu are 1 5 and 2 3 mm a respectively the rise of these islands is clogging the indo pacific seaway

reconciling regional continuity with local variability in structure uplift and exhumation of the timor orogen abstract along strike variations in orogenic development can be difficult to constrain resulting assumptions projecting similarity or variability along strike can lead to erroneous conclusions at the orogen scale young orogens provide opportunities to document limits of along strike projection and test factors that may control lateral variability here we present new constraints on the history of uplift exhumation and shortening in the timor orogen from west timor indonesia structural mapping documents a foreland thrust stack of jurassic miocene australian margin strata and a hinterland antiformal stack of permo triassic australian continental units duplexed below banda arc lithosphere biostratigraphy within the piggyback central basin reveals earliest deepwater synorogenic deposition at 5 57 5 53 ma uplift from lower to middle bathyal depths at 3 35 2 58 ma and uplift from middle to upper bathyal depths at 2 58 1 30 ma hinterland permo triassic strata yield apatite u th he ages of 0 33 2 76 ma apatite fission track ages of 2 19 3 53 ma and partially reset zircon u th he ages these thermochronology ages are youngest or most strongly reset in the center of the antiformal stack and yield modeled exhumation rates of 0 45 3 31 km myr a balanced cross section reveals a minimum of 300 km of shortening including 210 km of australian continental subduction below the banda forearc when compared to published results from timor leste these data show that the timing of initial collision synorogenic basin uplift and total shortening amount were broadly similar across the island therefore despite along strike changes in orogen morphology and significant small scale spatial variability in deformation first order structural similarity dominates at large scales we suggest that along strike variations in orogen morphology are due to changes in the distribution of deformation within the orogen driven by differences in backstop strength internal wedge strength and basal decollement friction as well as the presence of the wedge top central basin in west timor

from convergent plate margin to arc continent collision formation of the kenting melange southern taiwan abstract the kenting melange on the hengchun peninsula taiwan formed through tectonic shearing of subduction complex lithologies probably within the plate boundary subduction channel between the eurasian and philippine sea plates with further deformation and exhumation in the pliocene pleistocene during arc continent collision field relations reveal a structural gradation from normal stratified turbidite sequence mutan formation through broken formation to highly sheared kenting melange containing allochthonous polygenic blocks this gradation is consistent with an increase of average vitrinite reflection values from 0 72 in the mutan formation through 0 93 in the broken formation to 0 99 in the melange suggesting temperatures of at least 140 c during formation of the kenting melange zircons from gabbro in the kenting melange are dated as 25 46 0 18 ma which together with geochemical data constrains the source to south china sea oceanic lithosphere in combination with the field relationships vitrinite reflectance values microfossil stratigraphy and offshore geophysical data from s and se taiwan we propose that the kenting melange initially formed at the subduction plate boundary from off scraped trench deposits minor plio pleistocene microfossils

discovery of the early jurassic gajia melange in the bangong nujiang suture zone southward subduction of the bangong nujiang ocean melange records a series of geological processes associated with oceanic subduction and continental collision this paper reports for the first time the presence of early jurassic melange from nw nagqu in the southern margin of the bangong nujiang suture zone termed as the gajia melange it shows typically blocks in matrix structure with matrix of black shale and siliceous mudstone and several centimeters to several meters sized blocks of sandstone silicalite limestone and basalt the sandstone blocks consist of homologous sandstone and two types of exotic sandstone with different modal compositions the group 1 of exotic sandstone blocks consists of mainly of feldspar and quartz whereas the group 2 is rich in volcanic detritus the group 3 of homologous sandstone blocks is rich in feldspar and volcanic detritus with rare occurrence of quartz u pb age data and in situ hf isotopic compositions of detrital zircons from sandstone blocks are similar to those from the lhasa terrane suggesting that the sandstone blocks in the gajia melange most probably came from the lhasa terrane the yc1 2 age of homologous sandstone blocks is 177 2 4 ma suggesting an early jurassic depositional age for the sandstones within the gajia melange the gajia melange likely records the southward subduction of the bangong nujiang ocean during the early jurassic

seismic reflection patterns associated with continental convergent margins through time abstract the important role of tectonic wedging in accommodating horizontal shortening strain is increasingly recognized to occur at all scales within continental convergence zones wedge structures appear most common in accretionary orogens involving former passive margins with large volume turbidite sedimentary fans or accretionary prisms relatively small scale wedges can be recognized in outcrop but crustal scale wedge geometries must be observed and analysed using seismic reflection methods reflection profiles now exist across a large number of accretionary orogen settings of diverse ages and continents similarities in seismic patterns within the major eras enable creation of a series of stylised continental margin transects for each major time period relatively low rock strength found in turbidite sediments rich in micas especially when contrasted with strengths of igneous volcanic arc rocks plays a major role because it localizes thrust faults within weaker horizons schematic cross sections across accretionary margins that span five geological eras summarize the principal features interpreted on numerous seismic reflection sections important details vary such as the depths where tectonic wedging initiates but tectonic wedges of diverse scales are observed in all cross sections the percentage and degree of consolidation or metamorphism of turbiditic greywackes apparently controls the degree depth and scale of the crustal wedging

thermal history of australian passive margin cover sequences accreted to timor during late neogene arc continent collision indonesia abstract paleotemperature indicators and apatite fission track analysis of australian continental margin cover sequences accreted to the active banda arc continent collision indicate little to no heating during rapid late neogene uplift and exhumation thermal maturation patterns of vitrinite reflectance conodont alteration and illite crystallinity show that peak paleotemperatures ppt increase with stratigraphic and structural burial the highest ppt is found in the northern hinterland of the accretionary wedge which was beneath progressively thicker parts of the upper plate towards the north major discontinuities in the pattern of ppt are associated with the position of major thrust ramps such as those forming the ramelau kekneno arch rka ppt for upper triassic to neogene strata south of the rka are 60 80 c which are similar to and in many cases lower than correlative and age equivalent units drilled on the nw australian shelf permian to lower triassic sedimentary strata thrust over younger units within and north of the rka have ppt of 100 220 c thrust sheets accreted beneath the upper plate have ppt approximately 90 c higher than those frontally accreted metamorphism of the northernmost units of these sequences yield ppt of 300 c thrust stacking yields an inverted thermal profile of ppt decreasing discontinuously downward and to the south towards the foreland the timing of ppt is constrained by apatite fission track ages from mostly triassic continental margin cover sequences ages of upper triassic units are primarily coeval with deposition and show little evidence of thermal annealing whereas those of lower triassic units are almost completely annealed and range from 1 8 0 5 19 2 9 7 ma the clustering of apatite fission track ages into two distinct groups indicates that the upper boundary of the partial annealing zone has remained for some time at a triassic stratigraphic interval in the slope and rise of the nw australian continental margin the position of this zone on the present shelf is higher in the stratigraphic column due to the greater thickness of post breakup shelf facies units thrust stacking of rise slope and shelf units produces an inverted vertical profile of increasing apatite fission track age with depth lack of any long confined track lengths in apatite from all of the units requires rapid and recent exhumation of the thrust stack which is coincident with rapid phases of pliocene pleistocene exhumation documented throughout timor these data preclude pre late miocene tectonic burial or pre pliocene exhumation of the nw australian continental margin

the argille varicolori unit in lucania italy a record of tectonic offscraping and gravity sliding in the mesozoic tertiary lagonegro basin southern apennines

slumping and sliding in miocene and recent developing arc basins onshore and offshore sumba indonesia abstract neogene slidemasses in eastern sumba are discussed and compared to neogene and quaternary analogues in seismic profiles from the offshore lombok and savu basins the onshore examples were deposited in deep marine base of slope environments within the reach of large amounts of clastics derived from a volcanic arc i e in a setting comparable to that of the recent slides onshore three types of slides are distinguished ranging from mud clast rich debris flows type 1 their possible seismic origin is discussed elongate lenticular slumps type 2 to over 100 m thick slide masses of intimately mixed and folded strata together with rafts of less deformed sediments type 3 the offshore analogues may be twice as thick both in the field and in the seismic profiles such slides are found at various superimposed levels five superimposed units can be distinguished in a seismic profile in the savu basin near the westernmost extension of the offshore sumba ridge a giant blocky slide occurs all slide masses are located on slopes with increasing gradients due to differential vertical movements tectonically induced oversteepening is therefore considered a main cause of failure in outcrops the upper surfaces of the slides are almost flat this contrasts with a hummocky topography seen in some of the offshore examples

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

an evaporite bearing accretionary complex in the northern front of the betic rif orogen the guadalquivir accretionary complex forms a largely oblique prism at the northern edge of the betic rif orogen where miocene sediments plus allochthonous evaporite bearing units were accreted during the displacement of the alboran domain towards the west traditional interpretations end the tectonic structuring of the betic cordillera at the present topographic front beyond which gravitational and or diapiric processes would predominate however this study shows pervasive tectonic deformation in the outer prism with coherent oblique shortening kinematics which is achieved through an alternation of roughly n s arcuate thrust systems connected by e w transfer fault zones these structures accord well with the geophysical models that propose westward rollback subduction the main stage of tectonic activity occurred in the early middle miocene but deformation lasted until the quaternary with the same kinematics evaporite rocks played a leading role in the deformation as evidenced by the suite of ductile structures in gypsum distributed throughout the area s and l gypsum tectonites scaly clay fabrics and brittle fabrics coexist and consistently indicate westward motion top to 290 with subordinate n s contraction almost perpendicular to the transfer zones this work reveals ductile tectonic fabrics in gypsum as a valuable tool to elucidate the structure and deformational history of complex tectonic melanges involving evaporites above the decollement level of accretionary wedges

u pb dating of a terminal pliocene coral from the indonesian seaway abstract pristine detrital platygyra corals were discovered in an exhumed package of syn orogenic marine sediments on the island of timor in the eastern indonesian region and dated using u pb techniques a single coral from the upper part of the sequence yields a 238 u 206 pb 207 pb 206 pb concordia age of 2 66 0 14 2 ma that is supported by coral 87 sr 86 sr chemostratigraphy and foraminiferal biostratigraphy from bounding strata minor u series disequilibrium is best explained by u mobility within the last 150 ka as pore water chemistry was altered during exhumation and is unlikely to have affected 238 u 206 pb and the apparent sample age by more than 1 2 the ability to date corals beyond the limits of 14 c and u th techniques provides the opportunity to improve the temporal resolution of associated marine chronostratigraphic records in this instance we refine the timing of timor s emergence from beneath the waters of the indonesian seaway is and the initiation of turbiditic deposition at the study site to between ca 3 35 and 2 66 ma these results have implications for the evolution of topography and is oceanic pathways in the active orogenic belts along the northern fringes of the australian plate

plate kinematics origin and tectonic emplacement of supra subduction ophiolites in se asia abstract a unique feature of the circum pacific orogenic belts is the occurrence of ophiolitic bodies of various sizes most of which display petrological and geochemical characteristics typical of supra subduction zone oceanic crust in se asia a majority of the ophiolites appear to have originated at convergent margins and specifically in backarc or island arc settings which evolved either along the edge of the sunda eurasia and australian cratons or within the philippine sea plate these ophiolites were later accreted to continental margins during the tertiary because of fast relative plate velocities tectonic regimes at the active margins of these three plates also changed rapidly strain partitioning associated with oblique convergence caused arc trench systems to move further away from the locus of their accretion we distinguish relatively autochthonous ophiolites resulting from the shortening of marginal basins such as the present day south china sea or the coral sea and highly displaced ophiolites developed in oblique convergent margins where they were dismantled transported and locally severely sheared during final docking in peri cratonic mobile belts i e the philippine mobile belt we find a series of oceanic basins which have been slightly deformed and uplifted varying lithologies and geochemical compositions of tectonic units in these basins as well as their age discrepancies suggest important displacements along major wrench faults we have used plate tectonic reconstructions to restore the former backarc basins and island arcs characterized by known petro geochemical data to their original location and their former tectonic settings some of the ophiolites occurring in front of the sunda plate represent supra subduction zone basins formed along the australian craton margin during the mesozoic the philippine sea basin the huatung basin south of taiwan and composite ophiolitic basements of the philippines and halmahera may represent remnants of such marginal basins the portion of the philippine sea plate carrying the taiwan philippine arc and its composite ophiolitic continental crustal basement might have actually originated in a different setting closer to that of the papua new guinea ophiolite and then have been displaced rapidly as a result of shearing associated with fast oblique convergence

structural expression of forearc crust uplift due to subducting asperity abstract new structural observations and mapping of reefal terraces carried out both on the field and on satellite remote sensing data indicate that sumba island is presently undergoing a large amount of extension associated with a significant regional uplift this crustal uplift may have been created by a major thrust emerging in the south of the island the uplift which partly accommodated the australian plate south west banda arc convergence is associated with the general northeastward tilt of the island the consequent anomalous positive topography along the southern coast of the island is being compensated by significant tectonic erosion along large scale curvilinear normal faults in the southeastern half of the island the most important expression of this gravitational collapse is located at the receding side of an advancing circular dome showing striking similarities with accretionary wedges being affected by seamount subduction the part of the forearc basin known as the savu basin is moderately deformed mostly in its central part and appears to act as a rigid buttress in the convergence between the banda arc and the australian plate as a result the convergence appears to be transferred northward within the actively shortening back arc domain which goes from the north of the flores island to the southwest of the timor block the convergent plate boundary shows a transition between a stable domain west of sumba and a tectonized domain east of sumba the latter coinciding with the subduction of the outer australian passive margin the subduction of the ocean continent boundary of the austral indian plate below the banda arc since the lower pliocene may have incorporated some crustal fragments in the plunging benioff zone most likely the integration of the stretched continental lithosphere in the subduction zone caused the uplift the entire forearc domain exhibiting inherited structures of the upper plate

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

deformational styles in a sequence of olistostromal melanges pacific rim complex western vancouver island canada the pacific rim complex is exposed in a fault bounded slice along the west coast of vancouver island it is divided into two parts 1 the ucluth formation a basement unit composed of lower mesozoic arc volcanic rocks and 2 a suprajacent sedimentary sequence more than 2 km thick composed of lower cretaceous olistostromal melanges an unconformity is present at least locally at the ucluth melange contact and indicates that the ucluth formation is stratigraphic basement to the melanges melange style deformation is restricted to the sedimentary sequence and has affected virtually all parts of that sequence the melanges formed without the development of a cleavage or pervasive cataclasis indicating that deformation occurred prior to consolidation of the sediments three types of melanges have been recognized the first consists of a matrix of inter bedded mudstone chert sandstone and green tuff which encloses numerous exotic blocks of igneous rocks and limestone beds within the matrix show variable amounts of layer parallel fragmentation which is attributed to in situ liquefaction and lateral flowage within individual beds the blocks in this melange most of which were derived from the underlying ucluth formation are considered to be submarine slide blocks produced by rock falls from nearby basement scarps the matrix sediments near the blocks commonly contain wispy lenses of poorly sorted plutonic and volcanic detritus green tuff interpreted as scree from the rock slides the second and third types of melange are distinguished by the predominance of either mudstone or sandstone but are otherwise quite similar these melanges lack exotic blocks and consist of a contorted assemblage of mudstone turbidite sandstone conglomerate pebbly mudstone and rare chert all of which are depositionally interrelated sedimentary structures and stratal coherence are generally well preserved the internal structure of these melanges consists of a series of dismembered depositional sequences individual sequences are commonly more than 75 m thick some are upright and others are overturned paleoecological evidence indicates that some of these sequences were originally deposited in an infra slope basin thus these melanges are interpreted to have formed mainly by the accumulation of large slump sheets at the base of a submarine slope previous interpretations have considered the pacific rim complex to be a late mesozoic subduction complex constructed along the western margin of the wrangellia terrane vancouver island several factors argue against a subduction melange interpretation 1 the melanges were deposited on an older arc related basement not oceanic crust 2 exotic blocks were introduced as rock slides and not by subsurface faulting and 3 at least some of the strata originated in an infra slope basin the heterogeneous deformational style is more compatible with an origin by near surface mass movement processes including submarine slides rock falls debris flows and in situ liquefaction the amount of mass wasting recorded in the pacific rim melanges probably requires a seismically active setting where frequent ground shaking produced large transients in pore fluid pressure similarities in stratigraphy and metamorphism suggest that during late cretaceous time the pacific rim complex was part of the san juan cascades thrust system located 220 km to the southeast in northwestern washington state if this is correct the pacific rim melanges would have formed on the inboard side of wrangellia about 30 m y prior to the collision of wrangellia with the american continent the present location of the pacific rim outboard of wrangellia is attributed to younger latest cretaceous or early tertiary transcurrent displacement

perspectives on the roles of melanges in subduction accretionary complexes a review abstract melanges play three principal overlapping roles in the architecture of subduction accretionary complexes sacs during and after sac formation first tectonic melanges serve as zones of concentrated deformation within and below the accreted rocks that are assembled during the subduction accretion process these melanges facilitate preservation of inter melange less deformed accretionary units aus beneath the trench side of the sac the initial deformation zone along the decollement at the top of the down going plate is marked by non melange tectonically dismembered formations or thinner units of scaly rock and breccia that separate accreted rocks above from the subducting rocks below olistostromal rocks may be incorporated into the decollement here in the mid arc to inner arc areas of the sac exotic block bearing melanges develop in zones of tectonic fragmentation and mixing of accreting ocean plate stratigraphy in mud diapirs and along out of sequence faults some of which facilitate uplift of high pressure rocks and serpentinite matrix melanges second after accretion the sedimentary tectonic diapiric and polygenetic melange units serve as single block or sheet architectural aus or subunits within larger accreted aus of the sac diapiric melanges and sedimentary olistostromal melanges formed in and above sac fault blocks respectively may become incorporated into the sac during ongoing deformation and become architectural units as well third melanges serve as post subduction stress guides that focus shear strain during continuing and post accretion deformation of sacs allowing ongoing modification of the sac during progressive deformation of the orogen examples of each type of role reveal the importance of all three processes in the current architecture of outer orogenic belts

intrusive and extrusive micro melange couplets as distal effects of tidal pumping by a marine ice sheet microscopic soft sediment deformation structures in a 30 x 25 x 12 mm hand specimen of glaciogenic silty mudstone from the permo carboniferous dwyka formation of northern natal in south africa are illustrated by serial sections the processes these structures imply are interpreted using palinspastically restored sections and isopachytes reconstructed from them the sedimentation of silts muds and microrhythmites is found to have been punctuated by episodes of hydraulic activity which resulted in thirteen bodies with the mixed fabrics of micromelanges these are divisible into five melange types 1 subconcordant intrusive 2 disconcordant intrusive 3 subconcordant extrusive 4 near surface with asymmetric internal structures and 5 conformable near surface with internal structures symmetric about the palaeovertical remarkable similarities between isopachs for pairs of micromelanges at different levels in the specimen suggest that intrusive melanges at depth fed contemporaneous extrusive melanges on the sea floor each couplet of melanges with matched isopachs is linked by faults which are interpreted as having acted as hydraulic vents despite only parts of them being infilled by intrusive melange a significant proportion of the succession could consist of sediment recycled from depth by hydraulic extrusion repeated hydraulic intrusions along and extrusions from the same disturbed interface suggest that this interface acted as the distal leaking end of one of the hydraulic sills recently described by von brunn talbot 1986 pulses of pressurized water were transmitted through a prograding marine slope of quickclay by the tidal pumping of a marine ice sheet periodically grounding upslope the results of this analysis are extrapolated to processes operative in subduction complexes all four fabrics described from large scale hydraulic melanges in modern and ancient accretionary prisms are matched on a much smaller scale in our sample from a proglacial submarine slope dismember ment by faults is the only fabric element described from accretionary complexes which is missing from the micro analogues described here

resolving spatial heterogeneities in exhumation and surface uplift in timor leste constraints on deformation processes in young orogens although exhumation and surface uplift are important parameters in understanding orogenesis the opportunity to measure both in close proximity is rare in timor leste east timor deeply exhumed metamorphic rocks and piggyback deepwater synorogenic basins are only tens of kilometers apart permitting direct relation of uplift and exhumation by comparing micropaleontology to thermochronology interpreted through one dimensional thermal modeling foraminifera in two deepwater synorogenic basins suggest basin uplift from depths of 1 2 km to depths of 350 1000 m between 3 35 and 1 88 ma thermochronologic sampling was conducted in the central mountain belt between these basins of four muscovite 40ar 39ar samples one provides a reset age of 7 13 0 25 ma in the aileu high grade belt that suggests 9 16 km of exhumation since that time eighteen zircon u th he samples contain a group of reset ages in the aileu complex ranging from 4 4 to 1 5 ma which suggest exhumation rates of 1 0 3 1 mm yr with 2 7 7 8 km of exhumation since these ages thirteen apatite u th he ages in the gondwana sequence range from 5 5 to 1 4 ma suggesting 1 2 km of exhumation and defining a pattern of exhumation rates ranging from 0 2 to 1 3 mm yr that positively correlates with average annual rainfall seven apatite fission track samples display varying degrees of partial resetting with greatest resetting where apatite u th he ages are youngest together these data demonstrate extreme variability in surface uplift and exhumation over small spatial scales we propose ongoing subsurface duplexing driven by subduction and underplating of australian continental crust as the predominant driver for surface uplift and uplift induced exhumation

structural style of the offscraped ligurian oceanic sequences of the northern apennines new hypothesis concerning the development of melange block in matrix fabric shaly dismembered formations crop out extensively on the eastern side of the northern apennines as overthrusted cretaceous oceanic units the lack of metamorphism and the unconformably overlain epi ligurian sequence which represents the trench slope basin sedimentary sequence suggest that these units are accreted sequences accomplished by offscraping and imbrication these units are characterized by stratal disruption lack of internal coherence and complete destruction of the original stratigraphic sequence block in matrix fabric results in symmetric boudins and systematic presence of isolated or intrafolial hinges of isoclinal folds two orthogonal sets of tight to isoclinal folds are always recognizable involving the break up and the boudinage of the competent layers now transposed parallel to the axial planes of the disrupted isoclinal folds the superposition of two generations of orthogonal tight to isoclinal folds may be locally observed either in single bed fragments or in some preserved coherent units disruption and block in matrix fabric is a consequence of polyphase folding and intense shortening this geometry and kinematic interpretation well constrain the tectonic environment where these rocks were deformed to the proximity of the prism toe and within the prism itself thus the apennine broken formations result from the disruption of a sedimentary pile lying on the subducting plate of the cretaceous to eocene trench fore arc system which generated the ligurian accretionary wedge

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

mesozoic subduction accretion history in central tibet constrained from provenance analysis of the mugagangri subduction complex in the bangong nujiang suture zone

formation of an archean tectonic melange in the schreiber hemlo greenstone belt superior province canada implications for archean subduction accretion process the late archean circa 2750 2670 ma schreiber hemlo greenstone belt superior province canada is composed of tectonically juxtaposed fragments of oceanic plateaus circa 2750 2700 ma oceanic island arcs circa 2720 2695 ma and siliciclastic trench turbidites circa 2705 2697 ma following juxtaposition these lithotectonic assemblages were collectively intruded by synkinematic tonalite trondhjemite granodiorite ttg plutons circa 2720 2690 ma and ultramafic to felsic dikes and sills circa 2690 2680 ma with subduction zone geochemical signatures overprinting relations between different sequences of structures suggest that the belt underwent at least three phases of deformation during d1 circa 2695 2685 ma oceanic plateau basalts and associated komatiites arc derived trench turbidites and oceanic island arc sequences were all tectonically juxtaposed as they were incorporated into an accretionary complex fragmentation of these sequences resulted in broken formations and a tectonic melange in the schreiber assemblage of the belt d2 circa 2685 2680 ma is consistent with an intra arc right lateral transpressional deformation fragmentation and mixing of d2 synkinematic dikes and sills suggest that melange formation continued during d2 the d1 to d2 transition is interpreted in terms of a trenchward migration of the magmatic arc axis due to continued accretion and underplating the d2 intra arc strike slip faults may have provided conduits for uprising melts from the descending slab and they may have induced decompressional partial melting in the subarc mantle wedge to yield synkinematic ultramafic to felsic intrusions a similar close relationship between orogen parallel strike slip faulting and magmatism has recently been recognized in several phanerozoic transpressional orogenic belts suggesting that as in phanerozoic counterparts orogen parallel strike slip faulting in the schreiber hemlo greenstone belt played an important role in magma emplacement

evidence for the jurassic arc volcanism of the lolotoi complex timor tectonic implications abstract we report the first sensitive high resolution ion microprobe shrimp u pb zircon ages with geochemical data from metavolcanic rocks in the lolotoi complex timor the zircon u pb ages of two andesitic metavolcanic rocks yield a permissible range of the middle jurassic extrusion from 177 ma to 174 ma the geochemical data indicate that the origins of the basaltic and andesitic metavolcanic rocks are products of prolonged oceanic crust and arc magmatism respectively they are originated from partial melting of lherzolites providing an insight into the tectonic evolution of the forearc basements of the banda volcanic arc thus parts of the banda forearc basement are pieces of allochthonous oceanic basalts and jurassic arc related andesites accreted to the sundaland during the closure of mesotethys and are incorporated later into the great indonesian volcanic arc system along the southeastern margin of the sundaland

criteria helpful in recognizing shear zone and diapiric melanges examples from the hoh accretionary complex olympic peninsula washington a study of the middle miocene hoh melanges exposed on the western olympic peninsula washington provides criteria for differentiating between shear zone and diapiric melanges the shear zone melange is characterized by a consistent foliation orientation throughout the outcrop intense pervasive scaly foliation uniform fold vergence directions exotic clasts predominantly phacoidal clasts and consistent clast long axis lineations the diapiric melange is characterized by radial foliation in map view well developed scaly foliation at the contacts and poorly developed scaly foliation in the center of the melange opposite fold vergence directions across the melange and rare exotic clasts additionally clasts vary in shape from phacoidal at the contacts to angular in the center in the diapiric melange large clasts are found only in the center of the melange and clast long axes vary from tightly clustered at the contacts to near random orientations in the center the systematic variation in clast size in the diapir may be due to increased shear at the margins and or clast migration to the center of the diapir caused by a velocity viscosity contrast interpretation of field data indicates that some clasts rotate continuously in the matrix yet clast long axes have a definite preferred orientation this contradiction may be resolved by theoretical models indicating that clasts rotate fastest at high angles to the shear plane thus although clasts above a critical aspect ratio asymptotically approach stability parallel to the shear plane the long axes of rotating clasts spend a proportionally greater amount of time close to the shear plane parasitic folds in the matrix indicate that clast long axes align parallel to transport direction small scale folds in the matrix clast long axis lineations and the mean foliation indicate that the hogsback section of the hoh melange was emplaced by a high angle oblique thrust directed to n10 e

rise and fall of the eastern great indonesian arc recorded by the assembly dispersion and accretion of the banda terrane timor abstract new age petrochemical and structural data indicate that the banda terrane is a remnant of a jurassic to eocene arc trench system that formed the eastern part of the great indonesian arc the arc system rifted apart during eocene to miocene supra subduction zone sea floor spreading which dispersed ridges of banda terrane embedded in young oceanic crust as far south as sumba and timor in timor the banda terrane is well exposed as high level thrust sheets that were detached from the edge of the banda sea upper plate and uplifted by collision with the passive margin of nw australia the thrust sheets contain a distinctive assemblage of medium grade metamorphic rocks overlain by cretaceous to miocene forearc basin deposits new u pb age data presented here indicate igneous zircons are less than 162 ma with a cluster of ages at 83 ma and 35 ma 40ar 39ar plateau ages of various mineral phases from metamorphic units all cluster at between 32 38 ma these data yield a cooling curve that shows exhumation from around 550 c to the surface between 36 28 ma after this time there is no evidence of metamorphism of the banda terrane including its accretion to the edge of the australian continental margin during the pliocene these data link the banda terrane to similar rocks and events documented throughout the eastern edge of the sunda shelf and the banda sea floor

geodetic radio interferometric surveying applications and results very long baseline interferometry vlbi observations collected primarily under projects polaris polar motion analysis by radio interferometric surveying and iris international radio interferometric surveying since 1980 have been used to derive polar motion and ut1 time series the typical 24 hour observing sessions using the multistation north america europe network yield estimates of the x and y components of the pole with uncertainties of 1 2 milliseconds of arc mas and ut1 with uncertainties of 0 05 0 1 ms of time preliminary experimental results indicate that ut1 can be tracked by a single vlbi interferometer to the 0 1 ms level in observing periods of about 1 hour the same observations have been used to estimate the relative rates of motion of the north american and european tectonic plates and investigate possible regional deformations of the north american plate with uncertainties of a few millimeters per year check the accuracy of the adopted nutation series to the millisecond of arc level estimate earth tide love numbers for each observatory site with uncertainties of about 1 in h and 25 in l and determine the coordinates of 20 radio sources to a few milliseconds of arc temporal variations in the apparent positions of the radio sources caused by relativistic deflections of the radio signals in the solar gravitational field have been used to estimate the relativistic deflection parameter yielding a value of 1 000 0 003

untangling inconsistent magnetic polarity records through an integrated rock magnetic analysis a case study on neogene sections in east timor inconsistent polarity patterns in sediments are a common problem in magnetostratigraphic and paleomagnetic research multiple magnetic mineral generations result in such remanence haystacks here we test whether end member modeling of isothermal remanent magnetization acquisition curves as a basis for an integrated rock magnetic and microscopic analysis is capable of isolating original magnetic polarity patterns uppermost miocene pliocene deep marine siliciclastics and limestones in east timor originally sampled to constrain the uplift history of the young timor orogeny serve as case study an apparently straightforward polarity record was obtained that however proved impossible to reconcile with the associated biostratigraphy our analysis distinguished two magnetic end members for each section which result from various greigite suites and a detrital magnetite suite the latter yields largely viscous remanence signals and is deemed unsuited the greigite suites are late diagenetic in the cailaco river section and early diagenetic thus reliable in the viqueque type section by selecting reliable sample levels based on a quality index a revised polarity pattern of the latter section is obtained consistent with the biostratigraphy and unequivocally correlatable to the geomagnetic polarity time scale although the cailaco river section lacks a reliable magnetostratigraphy it does record a significant postremagnetization tectonic rotation our results shows that the application of well designed rock magnetic research based on the end member model and integrated with microscopy and paleomagnetic data can unravel complex and seemingly inconsistent polarity patterns we recommend this approach to assess the veracity of the polarity of strata with complex magnetic mineralogy

stratal disruption and development of melange western newfoundland effect of high fluid pressure in an accretionary terrain during ophiolite emplacement abstract the bay of islands ophiolite was emplaced onto the continental margin of north america during the mid ordovician taconic orogeny when tectonic slices of continental margin sediments were accreted to the moving allochthon tectonic slices grade into and are surrounded by melange early fracture in sandstones formed without grain breakage and allowed penetration of liquid petroleum along fracture planes other fractures involved cataclastic flow and were sometimes re activated during formation of later pressure solution cleavage shear fracture and extension fracture boudinage affect competent strata extensional veins cut cement in limestone beds and are filled by shale quartz calcite and bitumen folds also formed at a time when siltstone and sandstone were at least partially lithified melange matrix shows abundant shear and extension fractures in a variety of orientations coaxial extension responsible for disruption of bedding can be explained by a brittle accretionary wedge model in which high fluid pressures resulted from tectonic dewatering of shales surface slope decreased as fluid pressure rose beneath the ophiolite causing horizontal extension of the wedge after escape of excess water the surface slope steepened again as renewed stacking occurred

ocean trench blocked and obliterated by banda forearc collision with australian proximal continental slope abstract the bathymetry and abrupt changes in earthquake seismicity around the eastern end of the java trench suggest it is now blocked south east of sumba by the australian jurassic rifted continental margin forming the largely submarine roti savu ridge plate reconstructions have demonstrated that from at least 45 ma the java trench continued far to the east of sumba from about 12 ma the eastern part of the java trench called banda trench continued as the active plate boundary located between what was to become timor island then part of the australian proximal continental slope and the banda volcanic arc this banda trench began to be obliterated by continental margin arc collision between about 3 5 and 2 ma the present position of the defunct banda trench can be located by use of plate reconstructions earthquake seismology deep reflection seismology dsdp 262 results and geological mapping as being buried under the para autochthon below the foothills of southern timor locating the former trench guides the location of the apparently missing large southern part of the banda forearc that was carried over the australian continental margin during the final stage of the period of subduction of that continental margin that lasted from about 12 ma to about 3 5 ma tectonic collision is defined and distinguished from subduction and rollback collision in the southern part of the banda arc was initiated when the overriding forearc basement of the upper plate reached the proximal part of the australian continental slope of the lower plate and subduction stopped collision is characterised by fold and thrust deformation associated with the development of structurally high decollements this collision deformed the basement and cover of the forearc accretionary prism of the upper plate with part of the unsubducted australian cover rock sequences from the lower plate together with parts of the forearc basement they now form the exposed banda orogen the conversion of the northern flank of the timor trough from being the distal part of the banda forearc accretionary prism carried over the australian continental margin into a foreland basin was initiated by the cessation of subduction and simultaneous onset of collisional tectonics this reinterpretation of the locked eastern end of the java trench proposes that from its termination south of sumba to at least as far east as timor and probably far beyond the java banda trench and forearc overrode the subducting australian proximal continental slope locally to within 60 km of the shelf break part of the proximal forearc s accretionary prism together with part of the proximal continental slope cover sequence were detached and thrust northwards over the java banda trench and forearc by up to 80 km along the southwards dipping savu thrust and wetar suture these reinterpretations explain the present absence of any discernible subduction ocean trench in the southern banda arc and the narrowness of the forearc reduced to 30 km at atauro north of east timor

melange versus forearc contributions to sedimentation and uplift during rapid denudation of a young banda forearc continent collisional belt abstract new sedimentary geochemistry and petrographic analyses provide the most extensive sedimentary documentation yet of the rapid denudation of the young timor orogen the data from three basins including two widely separated well dated sections of the synorogenic megasequence of timor leste and a re dated dsdp 262 constrain the source and timing of detrital sediment flux during forearc continent collision along the timor sector of the banda arc the exhumed synorogenic piggy back basins formed above a melange unit that developed at the expense of a weak stratigraphic horizon in the mesozoic stratigraphy and was exhumed to the sea floor in latest messinian time following an interval of deep marine chalky marl sedimentation an increasingly muddy sediment flux indicates that the island of timor became emergent and shed sediment by 4 5 ma comparison of exhumed sections with similar patterns in the dsdp262 chemistry suggests that the sediment source was probably located some 50 60 km distant from the basin which is consistent with the aileu region of timor leste that shows an appropriate exhumation history all sedimentation between 4 5 and 3 2 ma was probably derived from a low relief rapidly eroding and mudstone dominated landscape with geochemical affinities to the triassic mudstone derived synorogenic melange the melange unit overlies and surrounds the banda terrane and was presumably structurally emplaced by propagation of a decollement through the triassic rocks during the collision after 3 2 ma sedimentation was dominated by hard rock lithologies of the banda terrane consisting of forearc cover and basement the latter including elements of metamafic rocks and metapelites this phase of sedimentation was accompanied by rapid uplift which may have been partly driven by a transient imbalance between rock uplift and denudation as resistant lithologies emerged from below melange like mudstone previous work has suggested that the timing of collision in timor leste and west timor was substantially different our reevaluation of dsdp 262 facies migration history in the context of the re dating presented here favours a relatively synchronous onset of uplift in both halves of the island but with different partitioning of strain between the foreland and hinterland in each half of the island

thrust related mudstone fabrics from the barbados forearc a backscattered scanning electron microscope study backscattered electron imaging on the scanning electron microscope has been used to examine the nature of microfabrics in mudstones from the barbados forearc samples from two important tectonic junctions in hole 671b of ocean drilling program leg 110 have been examined in detail at thrust a 128 m depth clays and clasts are pervasively aligned at about 50 to the thrust surface and a macroscopic scaly fabric is defined by anastamosing fractures in the decollement zone 500 550 m depth there is no preferred alignment of clays or clasts even though an irregular macroscopic scaly fabric is present scaly fabric in hole 671b is in part an artifact of specimen desiccation but may also reflect the release of anisotropic elastic strain relating to in situ stress conditions the disclosure that scaly fabric does not relate to grain alignment has profound implications for the nature of the barbados decollement seismic reflector the reflector does not correspond to a fabric anisotropy and is most likely to relate to the documented fluid flow anomaly in the decollement in contrast to scaly fabrics the microfabrics are the product of sediment deformation history the differences between the microfabrics at thrust a and those in the decollement probably relate to contrasts in deformation conditions in the decollement deformation probably occurred by paniculate flow under high pore fluid pressures where the individual panicles were aggregates of phyllosilicates at thrust a high pore fluid pressures were not maintained due to surface proximity enabling preconsolidation stresses to be exceeded as a result a pervasive phyllosilicate alignment has developed

deformation and exhumation in timor distinct stages of a young orogeny abstract timor island in the outer banda arc bordering the timor sea preserves the orogenic product of an arc continent collision between the australian plate and the banda arc that commenced after 10 9 9 8 ma gts2004 but emerged above sea level only 3 1 ma ago the orogenic pile includes large tracts of material from the australian margin including the permian to middle jurassic gondwana megasequence and the late jurassic to early late miocene australian margin megasequence which occur in thrust slices in addition material from the banda arc side of the plate margin referred to as the banda terrane occurs throughout the island and includes both seafloor metamorphosed igneous material and cover sediments also in thrust sheets however the distribution of thrust slices is unclear in many areas perhaps because only the uppermost nappes of the thrust pile are currently emergent and also because the thrust piles have been disrupted by later high angle faulting evidence from east timor suggests that the major break between deformed pre collisional strata and the relatively undeformed overlying deposits was during the late miocene 9 8 5 5 ma we present evidence for the timing of three distinct phases of orogenic development as determined from east timor including initial collision and emplacement of the early nappes creating loading and diapirism within the 9 8 5 5 ma interval a tectonic quiet interval 5 5 ma 4 5 ma that extended for about a million years during the middle of the collision and may represent the time of locking of the subduction system and a post 4 5 ma phase of uplift unroofing and further diapirism in response to isostatic rebound our conclusions offer an alternative model for the evolution of this part of the banda arc

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

nature and distribution of deformation across the banda arc australian collision zone at timor recently acquired seismic reflection and seamarc ii side scan and swath bathymetry profiles near timor show that the banda arc australia collision zone has a tectonic framework similar to that of a typical oceanic subduction system deformation is occurring at present most intensely at the foot of the inner slope of the timor trough this deformation front is discontinuously advancing southward as new thrust slices develop within the subducted australian margin strata in contrast present deformation is apparently negligible in the savu basin the complex fore arc basin north of timor a possible significant exception is a postulated right lateral northeast trending fault zone offsetting the outer arc high between savu and roti although back arc thrusting has been documented north of the volcanic arc this component of convergence is minor compared with the scale of ongoing deformation in the timor trough the detailed nature of these surveys has also led to the recognition of along strike variations in deformation in the timor trough and in the savu basin these variations may be related to the variable degree of involvement of the australian continental margin along the arc

late artinskian early kungurian early permian warming and maximum marine flooding in the east gondwana interior rift timor and western australia and comparisons across east gondwana abstract substantial new information is presented on upper artinskian kungurian deposits in timor leste and in the canning southern carnarvon and northern perth basins of western australia these basins situated between about 35 s and 55 s palaeolatitude formed part of the east gondwana interior rift a precursor to the rift that 100 my later formed the indian ocean in this region timor lay near the main axis of the east gondwana interior rift whereas the western australian basins were marginal splays from the rift axis the main depocentres developed as a result of faulting that was initiated during the late pennsylvanian detailed lithostratigraphic and biostratigraphic analyses have been made on the newly recognized bua bai limestone and the type cribas group in timor the noonkanbah formation in the canning basin the byro group in the merlinleigh sub basin of the southern carnarvon basin and the carynginia formation in the northern perth basin in timor the succession which is highly disrupted by faulting was deposited under open marine conditions probably in a shelf basin setting restricted very shallow water seas flooded the canning basin and the merlinleigh byro irwin sub basins of the southern carnarvon and northern perth basins and had highly variable oxygen levels and salinities typical of estuarine environments a similar pattern of warming and bathymetric change is recognized in all studied basins during the early part of the late artinskian cool conditions prevailed with water temperatures 0 4 c forming sea ice in the merlinleigh byro irwin rift rapid warming during the latter part of the late artinskian was accompanied by maximum marine flooding close to the artinskian kungurian boundary climatic and bathymetric conditions then allowed carbonate mounds with larger fusulines and a variety of algae to develop in the northern part of the rift system and tubiphytes conodonts and brachiopods with tethyan affinities to migrate into the marginal rift basins despite the generally adverse water quality at these depositional sites comparison between the stratigraphic record from the east gondwana interior rift and coeval records from lhasa and sibumasu indicate a similar pattern of climate change during the carboniferous to end cisuralian similar trends probably are present in eastern australia although there is confusion over the correlation of some units

stratigraphic constraints on suture models for eastern indonesia abstract although collision in eastern indonesia is now accreting the australian continent to southeast asia the small north and south banda oceanic basins within the suture zone are interpreted as late cenozoic extensional features stratigraphic columns from the surrounding islands conform to one of three generalised patterns two of which can be related to the margins of se asia sundaland and the australian continent respectively the third system which is dominant in the outer banda arc and eastern sulawesi is associated with a microcontinent that was rifted from australia in the jurassic drifted northwards ahead of australia in the cretaceous and collided with the sundaland margin in the paleogene subsequent collapse of the resulting collision orogen led to rapid extension and the formation of the banda sea behind the outer banda arc thrust belt eastern indonesia thus duplicates a pattern familiar in the mediterranean the tertiary compressional structures of the region cannot be explained solely in terms of the most recent collision which began only in the pliocene

fluid inclusion evidence for fluid mixing mascot jefferson city zinc district tennessee inverse correlation between homogenization temperature and salinity temperature of formation changes at near constant salinity and low salinity low to moderate temperature inclusion fluids are found in sphalerite formed in limestone an evolved basinal brine component was recognized by its characteristic temperature 100 degrees to 120 degrees c freezing point depression 1 fundamental chemical requirements for formation of pb zn ba f deposits from metal bearing basinal brines modified journal abstract

structural styles in mesozoic and cenozoic melanges in the western cordillera of north america the term melange is currently used to describe several different kinds of mudstone rich rocks that are broadly characterized by an obscure stratigraphy stratal disruption or a chaotic block in matrix fabric four types of melange which can be defined in outcrop on the basis of mesoscopic fabric and lithologic composition are particularly widespread and distinctive type i includes sequences of originally interbedded sandstone and mudstone that record incipient to thorough disruption and fragmentation of strata accomplished largely by layer parallel extension type ii consists of similarly deformed thin layers of green tuff radiolarian ribbon chert and minor sandstone originally interbedded with black mudstone disruption in both types i and ii which probably occurred while the sediments were incompletely consolidated has been ascribed to either imbricate faulting in accretionary wedges or gravitationally driven deformation type iii comprises inclusions of diverse shapes sizes and compositions enveloped in a locally scaly pelitic matrix the ultimate source of fragments is obscure because the majority were not derived by either the progressive disruption of interbedded sediments or in situ tectonic plucking and abrasion of adjacent rocks although some type iii melanges may have originated deep within accretionary prisms final emplacement as olistostromes muddy debris flow deposits or mud diapirs seems likely type iii melanges are mechanically analogous to scaly sheared serpentinites many probably have been tectonically remobilized or even intruded into shallow level fault zones type iv consists of lenticular inclusions bounded by an anastomosing network of subparallel faults their fabric records progressive slicing in brittle fault zones each of the four types of melange described here could in theory have formed in a variety of settings on or within an accretionary wedge at an active convergent margin none can yet be singled out as a uniquely diagnostic subduction melange

phanerozoic growth of asia geodynamic processes and evolution abstract accretion processes often obscured in mountain belts can be documented with great detail in se asia where these have taken place during the tertiary the resulting configuration showing accreted continental strips and tectonised wedges is illustrated by the tethysides jammed between the northern laurasian cratons baltica and siberia and gondwanian cratons africa arabia india and australia eurasia increased progressively in size due to the amalgamation of crustal and sedimentary belts at places where the processes are documented in the recent times they can be included within a collision factory which displays the opening of basins by rifting and sea floor spreading within the upper plate until they undergo a process of shortening both stages being subduction controlled in se asia the early stages are illustrated in the eastern sunda arc where the subduction of the sunda trench is blocked in sumba and timor region and flipped into the flores trough in less than 2 my the incipient shortening is at present taking place in the pliocene damar basins another stage where half of the upper plate basin has disappeared is documented in the celebes sea the examples of deformation being transferred further inland exist in the northern celebes sea and the makassar basin the next important stage is the complete consumption of the marginal basin where both margins collide and the accretionary wedge is thrust over the margin as illustrated in nw borneo and palawan each of these stages is responsible for a single short lived tectonic event the succession of several events composes an orogen which may last for over 10 my these events predate the arrival of the conjugate margin of the large ocean which marks the beginning of continental subduction as observed in the himalaya tibet region these examples show that the closure is generally diachronous through time as illustrated in the philippines we observe that the ophiolite obducted in such context is generally of back arc origin upper plate rather than the relict of the vanishing large ocean which is rarely preserved in the philippines once the crust is accreted the subduction zone progressively moved southward until its present position we propose that the lithospheric mantle of the accreted block is delaminated and rolls back in a continuous manner whereas the crust is deformed and accreted

on stress and strain in a continuous discontinuous shear zone undergoing simple shear and volume loss i summarise observations within a continuous discontinuous shear zone to discuss the local stress and strain conditions experienced within a mixed rheology shear zone undergoing volume loss and deformation approximating simple shear the chrystalls beach complex new zealand comprises phacoids formed from dismembered beds by layer parallel extension enclosed within a relatively incompetent matrix local extension is generally subparallel to the regional direction of shortening and overall it appears that layer parallel extension is a geometrical necessity in low angle shear zones where significant flattening occurs in response to simple shear accompanied by volume loss preferential stress loading of phacoids is predicted by fibre loading theory and the failure of phacoids by brittle fracture is thereby governed by fibre stresses transferred from the matrix the principal stress orientations in a phacoid are likely rotated relative to the matrix and either parallel or perpendicular to the phacoid matrix interface as preferential loading of phacoids decreases the stress level in the matrix an increased volume fraction of phacoids increases the strength of the shear zone as a whole however only small matrix volume fractions are required for the composite to act nearly as weak as the matrix 2012 elsevier ltd all rights reserved

deformation of the cablac mountain range east timor an overthrust stack derived from an australian continental terrace the cablac mountain range in central east timor comprises a thrust stack of gondwana megasequence rocks of mainly triassic to jurassic age this southerly directed thrust stack occurs in structural contact with the underlying lolotoi formation and both the lolotoi formation and the overlying gondwanan thrust stack appear to be structurally emplaced upon younger mid eocene units to the south in addition the cablac thrust stack is bound to the north by a high angle fault along which a crush breccia comprising clasts from both the gondwana megasequence and asian banda terrane occurs this interpretation of the cablac mountain range differs significantly from previous interpretations in which the cablac limestones were suggested to be massive miocene limestones that occurred in depositional contact with underlying units

the basins of sundaland se asia evolution and boundary conditions abstract most of the basins developed in the continental core of se asia sundaland evolved since the late cretaceous in a manner that may be correlated to the conditions of the subduction in the sunda trench by the end of mesozoic times sundaland was an elevated area composed of granite and metamorphic basement on the rims which suffered collapse and incipient extension whereas the central part was stable this promontory was surrounded by a large subduction zone except in the north and was a free boundary in the early cenozoic starting from the palaeogene and following fractures initiated during the india eurasia collision rifting began along large faults mostly n s and nnw sse strike slip which crosscut the whole region the basins remained in a continental fluvio lacustrine or shallow marine environment for a long time and some are marked by extremely stretched crust phu khanh natuna n makassar or even reached the ocean floor spreading stage celebes flores western sundaland was a combination of basin opening and strike slip transpressional deformation the configuration suggests a free boundary particularly to the east trench pull associated with the proto south china sea subduction java sulawesi trench subduction rollback in the early miocene australian blocks reached the sunda subduction zone and imposed local shortening in the south and southeast whereas the western part was free from compression after the indian continent had moved away to the north this suggests an important coupling of the sunda plate with the indo australian plate both to se and nw possibly further west rollback had ceased in the java sumatra subduction zone and compressional stress was being transferred northwards across the plate boundary the internal compression is expressed to the south by shortening which is transmitted as far as the malay basin in the late miocene most of the sunda plate was under compression except the tectonically isolated andaman sea and the damar basins in the pliocene collision north of australia propagated toward the north and west causing subduction reversal and compression in the short lived damar basin docking of the philippine plate confined the eastern side of sundaland and created local compression and uplift such as in nw borneo palawan and taiwan transpressional deformation created extensive folding strike slip faulting and uplift of the central basin and arakan yoma in myanmar minor inversion affected many thailand rift basins all the other basins record subsidence the uplift is responsible for gravity tectonics where thick sediments were accumulated sarawak ne luconia bangladesh wedge

the permian of timor stratigraphy palaeontology and palaeogeography the permian of timor in the lesser sunda islands has attracted the attention of palaeontologists since the middle of the nineteenth century because of the richness diversity and excellent state of preservation of its fauna these abundant fossil data have been compiled and updated for the present account the permian rocks of timor were deposited on the northern margin of australia at the present time the northern margin of australia in the region of timor is involved in a continent arc collision where australia is colliding with the banda arcs as a result of this collision permian rocks of the australian margin have been disrupted by folding and faulting with the generation of mud matrix melange and uplifted to form part of the island of timor due to this tectonic disruption it has proved difficult to establish a reliable stratigraphy for the permian units on timor especially as the classic fossil collections were obtained largely from the melange or purchased from the local people and do not have adequate stratigraphic control detailed systematic structural stratigraphic and sedimentological studies since the 1960s have provided a firmer stratigraphic and palaeogeographic background for reconsideration of the significance of the classic fossil collections permian rocks on timor belong either to a volcanic carbonate sequence maubisse formation or to a clastic sequence atahoc and cribas formations in which volcanics are less prominent the permian sequences were deposited on australian continental basement which was undergoing extension with spasmodic volcanic activity carbonates of the maubisse formation were deposited on horst blocks and volcanic edifices while clastic sediments of the atahoc and cribas formations were deposited in grabens the clastic sediments are predominantly fine grained derived from a distant siliciclastic source and are interbedded with sediments derived from the volcanics and carbonates of adjacent horst blocks bottom conditions in the graben were often anoxic in the present account events on timor during the permian are related to the regional tectonic context with the northward movement of australia leading to the amelioration of the climate from sub glacial to sub tropical together with the separation of crustal blocks from the northern australian margin to form the meso tethys

development of arc continent collision melanges linking onshore geological and offshore geophysical observations of the pliocene lichi melange southern taiwan and northern luzon arc western pacific abstract although the lichi melange has been studied intensively over the last decade its enigmatic nature has generated debates regarding its origin and evolution two prominent models have been proposed to explain the lichi melange the olistostrome model with slumping sediments and the tectonic collision model with intensive shearing neither model can explain what causes the interpreted slumping and complex faulting processes for the sediments here we study the lichi melange using a time space equivalence approach in which the tectonics of the offshore continuation of the lichi melange should represent an earlier stage in its evolution our study of marine multichannel seismic data suggested that the backthrusts in the accretionary prism propagate arcward above and within the deforming forearc and arc basement to incorporate the sediment and basement materials into the rear of the accretionary prism therefore we proposed the retrowedge evolution model whose novel key feature is that the irregular topography of the arc basement affects the taper angle of the retrowedge the retrowedge has a greater taper than the minimum taper of the prowedge so the slope can be steeper and thus favors gravitational failure such processes would generate complex faulting and slumping processes in the backthrusted forearc ridge and basin in sum this retrowedge model reconciles the mixture of slumping and faulting processes found in the lichi melange

structural anatomy of the ligurian accretionary wedge monferrato nw italy and evolution of superposed melanges we document in this study the internal structure of the late cretaceous late oligocene ligurian accretionary wedge in northwestern italy and the occurrence in this exhumed wedge of broken formation and three different types of melanges that formed sequentially through time the broken formation is the oldest unit in the accretionary wedge and shows bedding parallel boudinage structures which developed as a result of layer parallel extension at the toe of the internal part of the alpine wedge front during the late cretaceous middle eocene this broken formation experienced an overprint of tectonic diapiric and sedimentary processes as a result of continental collision in the late oligocene the ne vergent thrusting and associated shortening produced a structurally ordered block in matrix fabric through mixing of both native and exotic blocks forming the tectonic melange the concentration of overpressurized fluids along the thrust fault planes triggered the upward rise of shaly material producing the diapiric melange which in turn provided the source material for the downslope emplacement of the youngest late oligocene sedimentary melange the sedimentary melange units unconformably cover the collisional thrust faults constraining the timing of both this episode of contractional deformation related to continental collision and the combination and overlap of tectonic diapiric and sedimentary processes our multiscale structural analysis of the ligurian accretionary wedge shows that tectonic diapiric and sedimentary processes played a significant role in its evolution and that the interplay between and the superposition of these different processes strongly controlled the dynamic equilibrium of the accretionary wedge in the nw apennines western alps this kind of polygenetic melange development may be common in many modern and ancient accretionary complexes and the processes involved in their formation are likely to be responsible for major tsunamic events in convergent margins

accordion vs quantum tectonics insights into continental growth processes from the paleozoic of eastern gondwana the early paleozoic lachlan fold belt of eastern australia is widely regarded as an ancient convergent plate margin beneath which paleo pacific panthalassic oceanic lithosphere was continuously subducted it is cited as the type example of a retreating accretionary orogeny however sandstone compositions the sedimentological nature and timing of chert accumulation and overall stratigraphic architecture are not necessarily consistent with this model we suggest an alternative explanation for growth of gondwanan continental margin oceanic lithosphere outboard of the passive gondwana continental margin was subducted beneath an extensive intra oceanic island arc that now crops out as an allochthonous element macquarie arc within the fold belt once intervening oceanic lithosphere was eliminated this arc collided with and was emplaced upon the gondwana margin recognition of four such events along this margin through the phanerozoic suggests it is a significant mechanism for continental growth

provenance of permian triassic gondwana sequence units accreted to the banda arc in the timor region constraints from zircon u pb and hf isotopes abstract analysis of zircons from australian affinity permian triassic units of the timor region yield age distributions with large age peaks at 230 400 ma and 1750 1900 ma which are similar to zircon age spectra found in rocks from ne australia and crustal fragments now found in tibet and se asia it is likely that these terranes which are now widely separated were once part of the northern edge of gondwana near what is now the northern margin of australia the cimmerian block rifted from gondwana in the early permian during the initial formation of the neo tethys ocean the zircon age spectra of the gondwana sequence of ne australia and in the timor region are most similar to the terranes of northern tibet and malaysia further substantiating a similar tectonic affinity a large 1750 1900 ma zircon peak is also very common in other terranes in se asia hf analysis of zircon from the aileu complex in timor and kisar islands shows a bimodal distribution both radiogenically enriched and depleted in the gondwana sequence at 300 ma the magmatic event from which these zircons were derived was likely bimodal i e mafic and felsic this is substantiated by the presence of permian mafic and felsic rocks interlayered with the sandstone used in this study similar rock types and isotopic signatures are also found in permian triassic igneous units throughout the cimmerian continental block the permian triassic rocks of the timor region fill syn rift intra cratonic basins that successfully rifted in the jurassic to form the nw margin of australia this passive continental margin first entered the sunda trench in the timor region at around 7 8 ma causing the permo triassic rocks to accrete to the edge of the asian plate and emerge as a series of mountainous islands in the young banda collision zone eventually the australian continental margin will collide with the southern edge of the asian plate and these gondwanan terranes will rejoin

arc parallel extrusion of the timor sector of the banda arc continent collision structural studies of synorogenic basins in timor using field and remote sensing techniques provide new structural and geomorphic evidence for syn collisional extension in the converging plate boun

a preliminary case study of potential ceramic raw materials in the aileu area of timor leste abstract the newly independent country of timor leste is located in the eastern half of timor island indonesian archipelago geological studies of the country s mineral resources and extractive activities are practically non existent there is evidence of the exploitation of ceramic raw materials at outcrop level and two small brick kilns nowadays inactive in the dili and aileu areas near aileu there are light coloured silt rich deposits interpreted as overbank deposits interbedded with ancient river terraces post pliocene overlying metamorphic bedrock these sediments are the subject of this study which encompassed geological mapping and preliminary characterisation tectonically the area is a graben preserving alluvium and colluvium deposits five channel samples representative of the silt rich deposits were collected semi quantitative mineralogical analysis shows that the samples are made of illite quartz and kaolinite clays with accessory illite vermiculite interstratified minerals and k feldspar the chemical data show agreement with the estimated mineralogical composition the grain size distribution points to a silt dominated assemblage most samples have a satisfactory extrudability but deficient moulding properties after firing the sampled raw materials form a final product with possible ceramic capability for whiteware production

juxtaposed sequence stratigraphy temporal spatial variations of sedimentation and development of modern forming forearc lichi melange in north luzon trough forearc basin onshore and offshore eastern taiwan an overview abstract the south china sea oceanic lithosphere has been subducting eastward beneath the huatung basin philippine sea plate since the early miocene 18 ma the subduction is followed by the oblique collision between the luzon arc and the subducting eurasian plate from 6 5 ma the north luzon trough forearc strata and the luzon arc are then obducted northwestward as the coastal range eastern taiwan in the last 1 ma the collision propagates southward and is presently active in the region offshore se taiwan integrating seismic surveys offshore and a detailed forearc stratigraphy study onshore the coastal range this paper overviews the characteristics of forearc deformation dynamic sequence stratigraphy temporal spatial variations of forearc sedimentation and stratigraphic correlation onshore and offshore forearc sequences in response to the oblique convergent tectonics north of 20 n combining onshore and offshore forearc geology together allows us to reconstruct a structural evolution of the north luzon trough forearc basin from subduction through collision to obduction and to discuss the mechanism and processes responsible for developments of the modern forming forearc lichi melange during the active taiwan orogeny seismic surveys offshore show that forearc deformation in the subduction zone is primarily caused by increase of rear prism slope and west vergent thrusting of forearc strata along the prism top since the early forearc sedimentation east vergent backthrusting occurs during the late forearc sedimentation and propagates arcward when the volcanic arc collides with the accretionary prism in the collision zone bivergent thrusting leads to a development of the forearc huatung ridge popup as a bathymetric high which further controls the sedimentation of the younger forearc sequence in the collision zone in response to the syn sedimentation deformation forearc depocenter shifts progressively eastward forearc stratigraphy thus changes from two mega sequences bounded by an unconformity in the subduction zone to three mega sequences juxtaposed from west to east unconformably in the collision zone as a consequence the forearc deformation and stratigraphy in the oblique collision zone off se taiwan show a characteristic temporal spatial pattern that the lowest mega sequence with the most intensive deformation occurs restrictedly in the west whiles the middle and the upper mega sequences with mild deformation crop out in the center and the eastern part of the forearc basin respectively detailed biostratigraphy study using planktonic foraminifera and calcareous nannoplanktons indicates that the forearc strata onshore the coastal range are also composed of three sequences lower unit s 1 6 5 5 8 ma middle unit s 2 5 8 3 0 ma and upper unit s 3 a structure reconstruction reveals that the north luzon trough forearc strata have experienced multiple stages of thrust deformation from subduction through collision to obduction these deformations account for the mechanism and processes to develop the modern forming highly sheared ssz bearing forearc lichi melange tectonically in the western coastal range during the last 1 ma

geodynamic patterns of ophiolites and marginal basins in the indonesian and new guinea regions analysis of spatial temporal geological and geochemical patterns of ophiolites in the indonesian and new guinea region indicates a strong correlation with marginal basin development and closure the spatial distribution of ophiolites is mostly linked with marginal basin producing zones of oblique convergence and collision strain partitioning in these zones creates a series of ephemeral plate boundaries between several independently moving lithospheric blocks repeated disruption of the diffuse boundaries between the blocks by changes in plate motion and collision induced mantle extrusion creates space that is rapidly filled by new ocean basins in the upper plate of subduction zones suprasubduction zone ssz spreading of these basins is enhanced by episodic extrusion of asthenosphere escaping collisional suture zones various closure events and global plate motion changes are reflected in the temporal distribution of marginal basin and ophiolite ages most ophiolite slabs in the indonesian and new guinea region represent fragments of oceanic lithosphere with a subduction zone component as indicated by the common refractory petrochemistry of the mantle sequence and occurrence of boninite age and compositional heterogeneity may indicate that some ophiolite bodies are composite terranes collisions with buoyant lithosphere transfo parts of these ocean basins into ophiolites the connection between ophiolites and marginal basins is strongest where parts of actively spreading ssz basins are partially represented as ophiolites in collision zones many of the various tectonic models proposed for the origin and tectonic evolution of ophiolites are supported by plate interactions in the indonesian and new guinea region dewey bird 1970 silver smith 1983 moores et al 1984 searle stevens 1984 dilek moores 1990 harris 1992 dickinson et at 1996 however the geolo gical associations of these interactions remain poorly resolved allowing different parts of the region to be used as modern analogues for almost any tectonic scenario simple explanations based on plate kinematics alone fail to account for the increasing levels of complexity observed in the indonesian and new guinea region new ideas and supporting evidence for mantle extrusion mechanisms e g flower et at 2001 also rely heavily on descriptions of plate interactions in this region doglioni et at 1999 and raise new questions about how these processes may relate to the spatial and temporal pattern of ophiolites this paper provides a synthesis of the temporal and spatial patterns and tectonic associations of marginal basins and ophiolites throughout the indonesian and new guinea region it explores the relations between various plate boundary processes and ophiolite genesis and emplacement such as the role of strain partitioning trench rollback subduction polarity asymmetry astheno spheric flow and plate kinematics

earthquake occurrence along the java trench in front of the onset of the wadati benioff zone beginning of a new subduction cycle 1 spatial distribution of earthquake foci in the central part of the sunda arc was analyzed using global seismological data the analysis revealed the existence of a distinct strip of earthquakes distributed along the java trench separated by a trench parallel 50 150 km wide aseismic link from seismicity belonging to the wadati benioff zone of the recently subducting slab the seismicity pattern at the plate margin corresponds well with the morphology of the seafloor the along trench seismicity correlates with the position of the java trench and the onset of the wadati benioff zone correlates with the java trough the gps measurements performed in three analogous structural units of the neighboring sumatran convergent margin point to substantial differences in velocities of movement of the respective units and correlate with the spatial distribution of earthquake foci we interpret the distinct along trench seismicity as a consequence of the onset of a new subduction cycle due to the rapid convergent movement of the indo australian plate relative to the aseismic lithospheric link

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

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

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

melange production and the importance of shale diapirism in accretionary terrains although melanges are widely believed to form in subduction zones there is little agreement as to the mechanism by which the characteristic chaotic aspect of a melange develops1 2 debate centres on the relative effects of gravity sliding down the inner trench slope and shearing along thrust faults during offscraping or underplating2 3 the results of deep sea drilling and mapping of modern accretionary terrains4 combined with geophysical investigation of outer arc regions favour the thrust or fold packet model1 4 8 of accretion although some melange deposits exposed on land appear to fit an olistostrome model better1 9 shale diapirs and mud volcanoes are abundant in many modern accretionary terrains10 12 and probably form as a result of rapid overloading caused by tectonic thickening4 13 an investigation of extensive melange zones in northern irian jaya has now shown that they are the product of shale diapirism which suggests that shale diapirism is an important process in the tectonic mixing of accretionary terrains

mechanisms of subduction accretion as implied from the broken formations in the apennines italy mesoscale structural analysis of the ligurian broken formations of the northern apennines and the regional occurrence of subduction related structures indicate polyphase folding as the mechanism responsible for progressive disruption the evidence for direct correlation between regionally extensive noncylindrical folds and tectonic disruption has a strong bearing on determining how the ligurian accretionary prism evolved for example the block in matrix structure of the ligurian tectonic melanges is produced through extension developed along fold limbs in a compressive stress field as expected from offscraping and intraprism deformation the model implied by the mesoscale and macroscale analyses of the ligurian tectonic melanges provides one mechanism of accretion reconciling two deformation styles i e stratal disruption and folding commonly seen in ancient accretionary prisms furthermore this model could be relevant in active accretionary prisms especially in the intraprism part where the seismic and drilling data are sparse

plate boundary reorganization in the active banda arc continent collision insights from new gps measurements abstract new gps measurements reveal that large sections of the se asian plate are progressively accreting to the edge of the australian continent by distribution of strain away from the deformation front to forearc and backarc plate boundary segments the study was designed to investigate relative motions across suspected plate boundary segments in the transition from subduction to collision the oblique nature of the collision provides a way to quantify the spatial and temporal distribution of strain from the deformation front to the back arc the 12 sites we measured from bali to timor included some from an earlier study and 7 additional stations which extended the epoch of observation to ten years at many sites the resulting gps velocity field delineates at least three sunda arc forearc regions around 500 km in strike length that shows different amounts of coupling to the australian plate movement of these regions relative to se asia increases from 21 to 41 to 63 eastward toward the most advanced stages of collision the regions are bounded by the deformation front to the south the flores wetar backarc thrust system to the north and poorly defined structures on the sides the suture zone between the nw australian continental margin and the sunda banda arcs is still evolving with more than 20 mm yr of movement measured across the timor trough deformation front between timor and australia

re evaluation of the cablac limestone at its type area east timor revision of the miocene stratigraphy of timor abstract the cablac limestone widely recorded in timor has its type area on cablac mountain where it was regarded as a lower miocene shallow marine carbonate platform succession the bahaman like facies placed in the cablac limestone are now known to belong to the upper triassic lower jurassic rather than the lower miocene on the northern slopes of cablac mountain a crush breccia formerly regarded as the basal conglomerate of the formation is now considered to have developed along a high angle fault separating banda terrane units of asian affinity from an overthrust limestone stack containing units belonging to the gondwana and australian margin megasequences the cablac breccia includes rock fragments that were probably derived locally from these tectonostratigraphic units after terrane emplacement and overthrusting clasts include peloid and oolitic limestones of the upper triassic lower jurassic derived from the gondwana megasequence deep water carbonate pelagites of the cretaceous and paleogene derived from the australian margin megasequence upper oligocene lower miocene te letter stage shallow water limestone derived from the banda terrane and a younger neogene calcarenite containing clasts of mixed tectonostratigraphic affinity there is no evidence for significant sedimentary or tectonic transport of clasts that form the breccia the clast types and the present understanding of the geological history of timor suggest that the crush breccia formed late in the plio pleistocene uplift history of timor it is not the basal conglomerate of the cablac limestone however the clasts of an upper oligocene lower miocene limestone found in the breccia suggest that a shallow marine limestone unit of this age either outcrops in the region and has not been detected in the field or has been eroded completely during late neogene uplift the clasts are similar in age and lithology to an upper oligocene lower miocene formation that unconformably overlies a metamorphic complex in the booi region of west timor similar to the lolotoi metamorphic complex banda terrane that is juxtaposed against the crush breccia of cablac mountain the cablac limestone at its type area includes a mixed assemblage of carbonate rock units ranging in age from triassic to plio pleistocene and representing diverse facies as a formation the name cablac limestone should be discarded for a cenozoic unit the upper oligocene lower miocene shallow water limestone unit that is typified by outcrops in the booi region of west timor and that has contributed to clasts in the cablac breccia is informally named the booi limestone it is considered part of the allochthonous banda terrane of asian affinity and represents the only shallow marine lower miocene unit known from timor the only other miocene sedimentary unit known from timor includes carbonate pelagites designated the kolbano beds probably deposited on an australian continental terrace at water depths between 1000 and 3000 m on the northeastern edge of cablac mountain oolitic limestone and associated units of the gondwana megasequence the kolbano beds of the australian margin megasequence and the booi limestone and associated metasediments of the banda terrane were juxtaposed by a plio pleistocene high angle fault along which the cablac crush breccia formed

the parona chaotic complex a puzzling record of the messinian late miocene events in monferrato nw italy the parona chaotic complex pcc from monferrato nw italy is a melange composed of carbonate cemented blocks floating in a matrix of weakly consolidated mud breccias it forms a minor 1 km2 chaotic sedimentary body enclosed in a larger messinian melange that rests unconformably on older deposits and is followed again unconformably by pliocene sediments three main facies have been recognized in the blocks a bioclastic rudstones and coquinoid grainstones of early messinian age composed of oligotypic assemblages of gastropods and the brackish water bivalve cerastoderma mixed with shallow water marine biota mollusks corallinae algae benthic foraminifers echinoid fragments rare ahermatypic corals these sediments record shallow water carbonate sedimentation with episodic brackish incursions and show a peculiar diagenetic overprint selective dissolution of aragonitic grains and early dolomitic cements b monogenic breccias composed of clasts of coquinoid grainstones floating in a dolomitic microcrystalline matrix c polygenic conglomerates composed of rounded clasts of pre messinian pelagic sediments of lower messinian bioclastic carbonates and of messinian evaporitic carbonates finally a few blocks of strongly cemented micritic limestones interpreted as methane derived carbonates for the geochemical signature of the carbonate phases strongly depleted in 13c are present the matrix enclosing the blocks is a mud breccia containing centimeter sized clasts of marly sediments micropaleontological analyses have shown that lower messinian and upper tortonian planktic foraminifers are mixed with lower miocene oligocene and eocene forms the pcc results from complex processes involving 1 deposition of the peculiar sediments preserved in the blocks and 2 their dismemberment and mixing as for the depositional history composition of the blocks has allowed to sketch the following evolution a deposition of bioclastic rudstones and coquinoid grainstones that are interpreted as lower messinian carbonate platform deposits for their strong compositional and diagenetical similarity with the lower messinian carbonates cropping out in the mediterranean region the monferrato bioclastic sediments are the northernmost example of messinian shallow water carbonates yet known b deposition of monogenic breccias they formed during the evaporitic phase of the messinian that was accompanied by a relative sea level drop and by erosion of the previously deposited coquinas depositional and diagenetical processes during the evaporitic phase are also recorded by clasts of evaporitic carbonates in the polygenic conglomerates c deposition of polygenic conglomerates that are interpreted as upper messinian post evaporitic fan delta facies resulting from an important erosional phase after deposition this succession was dismembered in the blocks forming the present day melange geometry stratigraphic relationships and internal characteristics of the pcc point to an origin related to gravity driven phenomena triggered by tectonics however the faunal mixing in the mud breccias and the occurrence of blocks of methane derived carbonates suggest that mud diapirism also played a role for the genesis of the pcc this latter mechanism which has been poorly considered until now could also have been effective in the genesis of messinian chaotic deposits that extensively crop out in nw italy