ordovician ocean plate stratigraphy and thrust duplexes of the ballantrae complex sw scotland implications for the pelagic deposition rate and forearc accretion in the closing iapetus ocean abstract the ballantrae complex at bennane lea in sw scotland contains important ocean plate stratigraphy basalt chert mudstone sandstone in an accretionary prism that is associated with a classic ordovician ophiolite we used the ocean plate stratigraphy to sub divide the prism into 11 tectonic units to determine the depositional age of bedded cherts zircons were separated from 9 tuff beds from 6 different units all the tuffs have early to middle ordovician ages even though their present positions are mutually distant these ages are consistent with microfossil records of radiolaria and graptolites the stratigraphic structural relationships demonstrate that the ocean plate stratigraphy has been repeated by bedding parallel thrusts this is typical of a modern accretionary duplex we calculated the sedimentation rate of early to middle ordovician bedded cherts at bennane lea on the basis of u pb zircon ages obtained from several tuff beds the data indicate that the depositional rate 0 6 3 m myr was as slow as that of mesozoic cenozoic equivalents defined by radiolaria the age spectra of detrital zircons from ballantrae sandstones show prominent single peaks at ca 467 and 478 ma and a lack of precambrian zircons integration of our new zircon ages with published isotopic data and palaeo geographic maps indicates that the sandstones were deposited near an intra oceanic arc and far from any continent containing precambrian rocks the pelagic to clastic sediments at bennane lea were deposited in the closing iapetus ocean from ca 477 ma to ca 464 ma when they were accreted with the intra oceanic arc of ballantrae

from mesozoic rifting to apennine orogeny the gran sasso range italy the apennines are a low temperature accretionary prism generated by the west directed subduction of the adriatic ionian plate whose structural origin is still to be fully understood the highest and best exposed seg ment of the apennines the gran sasso range is here documented to unravel the tectonic history of the northern tip of gondwana it is located along a ne verging salient of thrust sheets decoupling the sedimentary cover of the subducting adriatic lithosphere field mapping and structural analysis along the e w trending left lateral transpressive segment of the salient highlight the interplay of the inherited mesozoic passive margin stratigraph ic and tectonic framework with the neogene contraction the rheological differences between the massive carbonate platform and the well bedded turbiditic and pelagic limestones determined along strike undulations of the thrusts geometries and fold styles during shortening heterogeneities are due to inherited syn and post rift mesozoic tectonics the gran sasso overturned anticline shows a backlimb anomalously tilted toward the foreland and we infer this dip as being related to a deeper back thrust of a triangle zone the pinching out of the foredeep sequence on the growth anticline forelimb dates the contractional phases of the region to the late messinian from the late pliocene to present the area has been uplifted and extended about 2 km by oblique normal faults cross cutting the accretionary prism some of them are seismically active as shown by the 2009 mw 6 3 l aquila earthquake

40ar 39ar constraints on obduction of the seram ultramafic complex consequences for the evolution of the southern banda sea on kaibobo w seram obduction of hot oceanic lithosphere produced high grade metamorphism and granite in overthrust continental crust 40ar 39ar plateau ages of 5 65 6 0 ma and 5 4 ma of muscovite and biotite from the sole among the youngest so far measured on single crystals indicate complete resetting of the ar isotope system chloritized biotite crystals gave disturbed spectra and younger ages single fusion on biotite from the granite gave an age of 5 5 ma time limits for the obduction exhumation history of the kaibobo complex and sole are approximated by simple 1d forward p t t modelling constrained by pt data and 40ar 39ar thermochronology c 400 c at 6 ma c 320 c at 5 5 ma best fit results indicate that the decelerating post emplacement exhumation of ophiolite and sole began 8 ma ago the rate during the first 1 ma of this uplift exceeded 7 5 mm a 1 undoing 8 ma of migration in the sw pacific and australian regimes of motion back tracks kaibobo to the site where obduction emplacement ended near the southeastern corner of the banda sea plate similar compositions and time settings of the kaibobo and n timor ophiolites lead us to postulate that during the early miocene slow rate spreading occurred in the oceanic lithosphere of the southern banda sea south of the current volcanic arc

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

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

sunda banda arc transition incipient continent island arc collision northwest australia the eastern sunda arc represents one of the few regions globally where the early stages of continent arc collision can be studied we studied along the western limit of the collision zone at the sunda banda arc transition where the australian margin collides with the banda island arc causing widespread back arc thrusting we present integrated results of a refraction wide angle reflection tomography gravity modeling and multichannel reflection seismic imaging using data acquired in 2006 southeast of sumba island the composite structural model reveals the previously unresolved deep geometry of the collision zone changes in crustal structure encompass the 10 12 km thick australian basement in the south and the 22 24 kmthick sumba ridge in the north where backthrusting of the 130 km wide accretionary prism is documented the structural diversity along this transect could be characteristic of young collisional systems at the transition from oceanic subduction to continent arc collision citation shulgin a h kopp c mueller e lueschen l planert m engels e r flueh a krabbenhoeft and y djajadihardja 2009 sunda banda arc transition incipient continent island arc collision northwest australia geophys res lett 36 l10304 doi 10 1029 2009gl037533

mantle flow induced crustal thinning in the area between the easternmost part of the anatolian plate and the arabian foreland e turkey deduced from the geological and geophysical data abstract eastern anatolia consisting of an amalgamation of fragments of oceanic and continental lithosphere is a current active intercontinental contractional zone that is still being squeezed and shortened between the arabian and eurasian plates this collisional and contractional zone is being accompanied by the tectonic escape of most of the anatolian plate to the west by major strike slip faulting on the right lateral north anatolian transform fault zone natfz and left lateral east anatolian transform fault zone eatfz which meet at karliova forming an east pointing cusp the present day crust in the area between the easternmost part of the anatolian plate and the arabian foreland gets thinner from north ca 44 km to south ca 36 km relative to its eastern eahp and western sides central anatolian region this thinner crustal area is characterized by shallow cpd 12 16 km very low pn velocities

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

blueschists eclogites and subduction zone tectonics insights from a review of late miocene blueschists and eclogites and related young high pressure metamorphic rocks abstract in this paper late miocene blueschist and eclogite belts including the world s youngest blueschist belt in timor tanimbar island chain eastern indonesia and the world s youngest coesite bearing eclogite papua new guinea together with selected cenozoic high pressure and ultrahigh pressure metamorphic rocks are reviewed from a synthesis of the geology metamorphism and chronology of these rocks the formation and exhumation process are evaluated and the significance on tectonics at convergent plate boundaries is discussed

accretion of the southern banda arc to the australian plate margin determined by global positioning system measurements global positioning system geodetic measurements at thirteen locations in indonesia and four in australia reveal that the australian continent has accreted the banda island arc to its margin small relative velocities of five sites on west java south kalimantan bali and south sulawesi define a rigid sunda shelf that moves relative to northern australia in a manner consistent with pole locations from nuvel 1 australia eurasia but at a rate that is about 7 slower block like northward motion of the southern banda arc toward the sunda shelf at nearly the same rate as australia suggests that the timor trough is now inactive as a thrust little of the convergence of australia with eurasia is accommodated by strain within the banda arc structure most of the convergence appears to occur as northward translation of the rigid arc with shortening on the flores and wetar thrusts and possibly on faults within the back arc basin

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

a dual doubly vergent orogen in the banda arc continent arc collision zone as observed on deep seismic reflection profiles new deep seismic reflection profiles across the banda arc of indonesia reveal reflectors in the uppermost 50 km of the lithosphere combined with existing earthquake hypocenter locations and focal mechanisms the new structural geometries inferred from the reflectors yield a more complete analysis of deformation during the past 10 m y and provide insights into how strain is partitioned across an orogenic belt in which volcanic arcs and continents converge a clearly defined wadati benioff zone and recent deformation of shelf sediments observed on older shallow seismic profiles indicated to previous workers that substantial convergence occurred at the timor trough a few focal mechanisms seafloor escarpments and recent geodetic surveying indicate that convergence at 7 cm yr 1 currently last 200 kyr occurs at the northern margin of the now inactive volcanic arc the wetar thrust zone reflectors on the new seismic profiles are interpreted as thrust faults and folds that occur throughout the crust and within the uppermost mantle between the timor trough and wetar thrust specifically basement reflectors beneath the toe of the accretionary complex have reverse sense offsets that imply blind thrusts the whole crust is horizontally shortened not only the sedimentary cover rocks that previously deformed into duplexes above a decollement reflectors dipping away from both margins of the forearc basin and at the northern margin of the volcanic arc are interpreted as evidence of thrusting thus each arc represents a doubly vergent fold and thrust belt but only the northern one is currently active crustal thicknesses inferred from seismic velocities reflectors and gravity anomalies are consistent with the merging of a thinned continental shelf margin with oceanic lithosphere to form an orogenic belt with at present 3 4 km of topographic relief in the region of eastern timor

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

cordierite bearing schists and gneisses from timor eastern indonesia p t conditions of metamorphism and tectonic implications in the boi massif of western timor the mutis complex which is equivalent to the lolotoi complex of east timor is composed of two lithostratigraphical components various basement schists and gneisses and the dismembered remnants of an ophiolite cordierite bearing pelitic schists and gneisses carry an early mineral assemblage of biotite garnet plagioclase al silicate but contain no prograde muscovite sillimanite occurs in a textural mode which suggests that it replaced and pseudomorphed kyanite at an early stage and some specimens of pelitic schist contain tiny kyanite relics in plagioclase textural relations between and mineral chemistries of ferro magnesian phases in these pelitic chists and gneisses suggest that two discontinuous reactions and additional continuous compositional changes have been overstepped possibly with concomitant anatexis as a result of decrease in pload during high temperature metamorphism the simplified reactions are garnet and or biotite sillimanite quartz cordierite hercynite ilmenite excess components p t conditions during the development of the early mineral assemblage in the pelitic gneisses are estimated to have been p 10 kbar and t 750 c based upon the plagioclase garnet al silicate quartz geobarometer and the garnet biotite geothermometer p t conditions during the subsequent development of cordierite bearing mineral assemblages in the pelitic gneisses are estimated to have been p 5 kbar and t 700 c with xh2o 0 5 based upon the fe content of cordierite occurring in the assemblage quartz plagioclase sillimanite biotite garnet cordierite coexisting with melt final equilibration between some of the phases suggests that conditions dropped to p 2 3 kbar and t 600 c a similar exhumation p t path is suggested for the pelitic schists with early metamorphic conditions of p 6 2 kbar and t 745 c and subsequent development of cordierite under conditions in the range p 3 4 kbar and t 600 700 c the tectonic implications of these p t estimates are discussed and it is concluded that the p t path followed by these rocks was caused by decompression during rifting and synmetamorphic ophiolite emplacement resulting from processes during the initiation and development of a convergent plate junction located in southeast asia during late jurassic to cretaceous time

world s youngest blueschist belt from leti island in the non volcanic banda outer arc of eastern indonesia abstract the timor tanimbar region constitutes part of the non volcanic outer banda arc of eastern indonesia here the world s youngest a type high pressure metamorphic belt crops out with different stages of evolution whereas an advanced domal uplift stage is seen in timor island the high pressure hp metamorphic belt is still in the first stage of tectonic extrusion on the eastern small islands of kisar leti moa sermata and laibobar the metamorphic rocks on leti are among the best exposed in the islands they are tectonically juxtaposed against overlying ultramafic rocks and underlying unmetamorphosed continental shelf sediments bound by normal and reverse faults respectively the leti metapelites display four progressive metamorphic zones chlorite biotite garnet chloritoid staurolite and kyanite zones with increasing grade zonation in leti metabasite unit is comparable and progressively changes from blueschist greenschist transition bs gs through epidote amphibolite ea to amphibolite am facies with increasing grade the highest grade metapelites and metabasites occupy structurally intermediate levels overprinting mineral relationships in bs gs transition schists indicate that decompression occurred from 5 5 7 kbar to the protoliths of leti metamorphic rocks are originally permo triassic the younger sediments and igneous rocks at the margin of the northward advancing australian continent entered the subduction zone immediately prior to the commencement of the banda arc australia collision in the pliocene burial reached a maximum depth of 30 35 km at the main stage of peak p t conditions and was related to the main stage of the collisional event slab break off at depth in the collision zone facilitated rapid uplift by wedge extrusion and active erosion during the exhumation stage the tectonic juxtaposition of the schist units at mid crustal levels and hydration may correspond to the final stage of barrovian overprinting which continued through transportation from depth the leti island belongs to the eastern portion of the world s youngest blueshist belt which has not yet entered the second stage mountain building and is slightly younger than the western timor which evolved to the extensive mountain building stage by doming

on meteorologically induced flushing in three u s east coast estuaries abstract meteorologically induced exchange with the coastal ocean is examined for three u s east coast estuaries using time series of subtidal volume flux over a common five month period a volume of water equal to that of the estuary was discharged every 86 4 135 3 and 108 8 days for narragansett delaware and chesapeake bays respectively however a large fraction of the water discharged to the shelf is recirculated ocean water for chesapeake bay outflowing estuarine water can be considered as a mixture of 2 4 3 0 water of mean estuarine salinity and the remainder water of oceanic salinity the degree of meteorological flushing is strongly influenced by mean depth as a drop in sea level of a given amplitude will force a greater fraction of water from a shallow estuary than from a deep system the relative importance of the meteorologically forced circulation and the gravitational circulation is frequency dependent as illustrated by salinity variance at the entrance to chesapeake bay seasonal salinity variance must ultimately be controlled by seasonal changes in runoff through the mechanism of gravitational circulation however the high coherence of wind induced changes in bay volume and bay entrance salinity at periods of 2 20 days suggests that meteorologically forced advection is primarily responsible for salinity variance at these time scales

seeing a mountain in a grain of garnet the collision of continents which results in mountain formation takes place through subduction in which one slab of crust is pushed below another the rock that is subducted is put under high pressure and new mineral phases can form as discussed in the perspective by liou et al a report by darling et al in the same issue p 91 1 describes a low pressure mineral cristobalite that was found in high pressure rocks understanding how this low pressure form of silicate was created and preserved may lead to better understanding of the process of subduction and how deep material is brought to the surface 1 lookup doi 10 1126 science 276 5309 91

buoyancy driven rapid exhumation of ultrahigh pressure metamorphosed continental crust abstract preservation of ultrahigh pressure uhp minerals formed at depths of 90 125 km require unusual conditions our subduction model involves underflow of a salient 250 150 km wide 90 125 km long of continental crust embedded in cold largely oceanic crust capped lithosphere loss of leading portions of the high density oceanic lithosphere by slab break off as increasing volumes of microcontinental material enter the subduction zone buoyancy driven return toward midcrustal levels of a thin 2 15 km thick low density slice finally uplift backfolding normal faulting and exposure of the uhp terrane sustained over 20 million years rapid 5 mm year exhumation of the thin aspect ratio uhp sialic sheet caught between cooler hanging wall plate and refrigerating downgoing lithosphere allows withdrawal of heat along both its upper and lower surfaces the intracratonal position of most uhp complexes reflects consumption of an intervening ocean basin and introduction of a sialic promontory into the subduction zone uhp metamorphic terranes consist chiefly of transformed yet relatively low density continental crust compared with displaced mantle material otherwise such complexes could not return to shallow depths relatively rare metabasaltic metagabbroic and metacherty lithologies retain traces of phases characteristic of uhp conditions because they are massive virtually impervious to fluids and nearly anhydrous in contrast h2o rich quartzofeldspathic gneissose schistose more permeable metasedimentary and metagranitic units have backreacted thoroughly so coesite and other uhp silicates are exceedingly rare because of the initial presence of biogenic carbon and its especially sluggish transformation rate uhp paragneisses contain the most abundantly preserved crustal diamonds

postcollision extension in arc continent collision zones eastern indonesia postcollisional extension superimposed on arc continent collision complexes is a common feature in the orogenic belts of eastern indonesia in the southern banda arc the arc continent collision event is essentially a pliocene and younger feature but already an element of extension is being superimposed on the compressional structures of the collision complex it is thus likely that the extension commences within a very short period 5 m y after the initiation of collision related compressional deformation a similar history of fold belt development immediately followed by extension can be inferred for the lengguru fold belt and the adjacent wandamen wondiwoi terranes of irian jaya and for the gulf of bone in sulawesi it is suggested that the extension results from decoupling of the subducting oceanic lithosphere from the unsubductable continental lithosphere and that the superimposition of extension is a virtually unavoidable consequence of the arc continent collision

quaternary hinterland evolution of the active banda arc surface uplift and neotectonic deformation recorded by coral terraces at kisar indonesia abstract coral terrace surveys and u series ages of coral yield a surface uplift rate of 0 5 m ka for kisar island which is an emergent island in the hinterland of the active banda arc continent collision based on this rate kisar first emerged from the ocean as recently as 450 ka these uplifted terraces are gently warped in a pattern of east west striking folds these folds are strike parallel to more developed thrust related folds of similar wavelength imaged by a seismic reflection profile just offshore this deformation shows that the emergence of kisar is influenced by forearc closure along the south dipping kisar thrust however the pinnacle shape of kisar and the protrusion of its metamorphic rocks through the forearc basin sediments also suggest a component of extrusion along shear zones or active doming coral encrusts the island coast in many locations over 100 m above sea level terrace morphology and coral ages are best explained by recognizing major surfaces as mostly growth terraces and minor terraces as mostly erosional into older terraces all reliable and referable coral u series ages determined by mc icp ms correlate with marine isotope stage mis 5e 118 128 ka the only unaltered coral samples are found below 6 m elevation however an unaltered tridacna giant clam shell in growth position at 95 m elevation yields a u series age of 195 31 ka which corresponds to mis 7 this age agrees with the best fit uplift model for the island loose deposits of unaltered coral fragments found at elevations between 8 and 20 m yield u series ages of

microearthquake seismicity and fault plane solutions related to arc continent collision in the eastern sunda arc indonesia the collision of australia with the eastern sunda and banda arcs of indonesia represents a modern example of the early stages of arc continent collision in order to obtain a more detailed view of the tectonics of the collision zone a microearthquake survey was conducted around the savu sea the region that encompasses the transition from subduction of indian ocean lithosphere on the west to collision or subduction of australian continental litho sphere on the east intermediate depth earth quakes were concentrated near pantar island the easternmost active volcano of the sunda arc and outline a northwest dipping zone that strikes n65oe from 70 to 150 km depth the seismic zone probably marks the western edge of the collision zone and its more northerly strike and the orientations of nodal planes from fault plane solutions indicate a 25 o bend in the subducted slab to a depth of at least 150 km because the convergence rate and the timing of collision from geologic observations on timor suggest that the oart of the slab now at 150 km depth was at the trench when australia first collided with timor we infer that continental crust or at least rifted continental margin crust caused the bend in the convergent margin and has been subducted to 150 km depth fault plane solutions of several events show nearly vertical nodal planes that trend parallel to the strike of the seismic zone along which a northwest side down sense of dis placement is indicated these events are concentrated at the southern top side of the seismic zone and suggest that the subducted lithosphere is presently detaching in the 50 100 km depth range beneath the eastern savu sea fault plane solutions for earthquakes within the upper part of the detaching slab 70 100 km depth have p and t axes whose trends lie parallel to the strike of the seismic zone and horizontal southeast trending b axes these earthquakes are interpreted as due to stresses caused by the bend in the subducting plate

a new petrogenetic grid for low grade metabasites abstract we have used internally consistent thermodynamic data to present calculated phase equilibria for the system na2o cao mgo al2o3 sio2 h2o ncmash in the range 0 500 c and 0 1 10 kbar involving the phases anorthite glaucophane grossular heulandite jadeite laumontite lawsonite paragonite prehnite pumpellyite stilbite tremolite wairakite zoisite with excess albite clinochlore quartz and pure water average activity terms derived from published mineral chemical data were included for clinochlore glaucophane prehnite pumpellyite tremolite and zoisite the new petrogenetic grid delineates stability fields and parageneses of common index minerals in zeolite prehniteactinolite prehnite pumpellyite pumpellyite actinolite blueschist and greenschist facies metabasites the stability fields of mineral assemblages containing prehnite pumpellyite epidote actinolite albite chlorite quartz were analysed in some detail using activity data calculated from five specific samples for example the prehnite actinolite facies covers a p t field ranging from about 220 to 320 c at pressures below 4 5 kbar the transition from the prehnite actinolite and pumpellyite actinolite to greenschist facies occurs at about 250 300 c at 1 3 kbar and at about 250 350 c at 3 8 kbar p t fields of individual facies overlap considerably due to variations in chemical composition

study on the structural characteristics of the overburden under thick loose layer and thin bed rock for safety of mining coal seam the geological conditions of the first working face at the baodian coal mine of the yanzhou mining district in china are examined to determine the feasibility of modifying coal pillars that prevent water seepage to those that prevent sand flow the coal pillars are under a thick loose layer of sediment and thin layer of bedrock after analyzing the structure of the rock and soil mass above the coal seam the thickness of the bedrock bottom clay layer and bottom aquifer of two detecting roadways are discussed at the center of the xingxing anticline the thinnest of the bedrock is only about 30 m however the thickness of the bottom clay layer is at least 10 m and more and the jurassic rock sandstone is the thinnest with low levels of water and a layer of weathered material the bottom aquifer has low water yield with no pressure the similarity theory is used to construct a prototype with 30 m high bedrock the conclusion is that the height of the caved zone height is about 21 3 m after the complete extraction of no 3 coal seam and the results are in agreement with the experimental data the results show that it is feasible for the first working face to use a coal pillar to prevent sand flow moreover the findings in this study can act as an important reference source for predicting the height of the overburden that would cause damage and reasonable advancement of mining that is considered to be safe under similar geomining conditions

on going orogeny in the outer arc of the timor tanimbar region eastern indonesia abstract the timor tanimbar islands of eastern indonesia form a non volcanic arc in front of a 7 km deep fore arc basin that separates it from a volcanic inner arc the timor tanimbar islands expose one of the youngest high p t metamorphic belts in the world providing us with an excellent opportunity to study the inception of orogenic processes undisturbed by later tectonic events structural and petrological studies of the high p t metamorphic belt show that both deformation and metamorphic grade increase towards the centre of the 1 km thick crystalline belt kinematic indicators exhibit top to the north sense of shear along the subhorizontal upper boundaries and top to the south sense in the bottom boundaries of the high p t metamorphic belt overall configuration suggests that the high p t metamorphic rocks extruded as a thin sheet into a space between overlying ophiolites and underlying continental shelf sediments petrological study further illustrates that the central crystalline unit underwent a barrovian type overprint of the original high p t metamorphic assemblages during wedge extrusion and the metamorphic grade ranged from pumpellyite actinolite to upper amphibolite facies quaternary uplift marked by elevation of recent reefs was estimated to be about 1260 m in timor in the west and decreases toward tanimbar in the east in contrast radiometric ages for the high p t metamorphic rocks suggest that the exhumation of the high p t metamorphic belt started in western timor in late miocene time and migrated toward the east thus the tectonic evolution of this region is diachronous and youngs to the east we conclude that the deep seated high p t metamorphic belt extrudes into shallow crustal levels as a first step followed by doming at a later stage the so called mountain building process is restricted to the second stage we attribute this quaternary rapid uplift to rebound of the subducting australian continental crust beneath timor after it achieved positive buoyancy due to break off of the oceanic slab fringing the continental crust in contrast tanimbar in the east has not yet been affected by later doming a wide spectrum of processes starting from extrusion of the high p t metamorphic rocks and ending with the later doming due to slab break off can be observed in the timor tanimbar region

mechanism and tectonic implications of the great banda sea earthquake of november 4 1963 abstract the banda sea earthquake of november 4 1963 h 100 km mb 7 8 is probably one of the largest intermediate depth shocks to have occurred worldwide this century the mechanism of this earthquake is studied in detail on the basis of p wave first motion surface wave and aftershock data from the analysis of long period multiple surface waves a seismic moment of 3 1 1028 dyn cm is obtained which is the largest reported so far for any intermediate or deep focus shock this value together with the estimated fault area of 90 70 km2 gives an average dislocation of 7 0 m and a stress drop of 120 bar this event represents an oblique thrust movement on a plane with dip direction n170 e dip 48 and rake 52 a geometrical consideration for the fault plane and the configuration of the inclined seismic zone beneath the banda arc suggests almost definitely that the large scale faulting took place within the subducted plate and offset it further repetition of such large scale faulting might eventually break the subducted plate the 1963 banda sea earthquake thus represents a seismological manifestation of the large scale deformation of the subducted plate in the mantle

thermobaric structure of the franciscan complex in the pacheco pass region diablo range california examination of the thermobaric structure of jadeite glaucophane bearing franciscan rocks in the pacheco pass region of the diablo range show that they are subhorizontal and the structurally intermediate horizon has the highest metamorphic grade mineral parageneses of more than 700 metagraywackes plus 38 metagraywacke samples from up to 1200 vertical feet of drill core were examined modal compositions of about 100 metagraywackes were determined and more than 2600 microprobe analyses were completed to quantify compositions of jadeitic pyroxene from about 80 metagraywackes the jadeite jd zone is defined by the assemblage jadeitic clinopyroxene quartz pm albite lawsonite pm sodic amphibole pm aragonite this zone occurs at an intermediate structural position sandwiched between subhorizontal jadeitic clinopyroxene free albite ab zones transition zones occur both above and below the jd zone the jd zone covers an area 20 km wide and 400 m thick the nearly flat lying boundaries betwee