late cenozoic geodynamic evolution of eastern indonesia this paper presents an internally and globally consistent model of plate evolution in eastern indonesia from middle miocene to present time it is centered on the banda sea region located in the triple junction area between the pacific philippine australia and south east asia plates the geological and geophysical data available from indonesia were until recently insufficient to define a unique plate tectonic model in this paper the new data taken into account clearly restrict the possible interpretations owing to a great number of geological geophysical and geochemical studies the major plate boundaries the sunda banda subduction zone to the south the tarera aiduna fault zone and the seram thrust to the east and the sorong fault zone and molucca sea collision zone to the north are now clearly identified the age of the major tectonic structures is also better known geodetic measurements well constrain the present time plate kinematics we also consider the deformation history within eastern indonesia where numerous short lived microplates and their related microcontinents successively accreted to the asiatic margin moreover magnetic anomalies identification of the north and south banda sea basins allows a precise kinematic reconstruction of the back arc opening we used the plates software to test the coherency of our model presented as a series of 4 plate reconstruction maps from 13 ma to the present finally the origin of oceanic domains restored by our reconstruction is discussed

influence of surface topography on the critical carbon dioxide level required for the formation of a modern snowball earth abstractthe influence of continental topography on the initiation of a global glaciation i e snowball earth is studied with both a fully coupled atmosphere ocean general circulation model aogc

rolling open earth s deepest forearc basin the weber deep a 7 2 km deep forearc basin within the tightly curved banda arc of eastern indonesia is the deepest point of the earth s oceans not within a trench several models have been proposed to explain the tectonic evolution of the banda arc in the context of the ongoing ca 23 ma present australia southeast asia collision but no model explicitly accounts for how the weber deep achieved its anomalous depth here we propose that the weber deep formed by forearc extension driven by eastward subduction rollback substantial lithospheric extension in the upper plate was accommodated by a major previously unidentified low angle normal fault system we name the banda detachment high resolution bathymetry data reveal that the banda detachment is exposed underwater over much of its 120 km down dip and 450 km lateral extent having produced the largest bathymetric expression of any fault discernable in the world s oceans the banda arc is a modern analogue for highly extended terranes preserved in the many regions that may similarly have rolled open behind migrating subduction zones

tectonometamorphic evolution of seram and ambon eastern indonesia insights from 40ar 39ar geochronology the island of seram eastern indonesia experienced a complex neogene history of multiple metamorphic and deformational events driven by australia se asia collision geological mapping and structural and petrographic analysis has identified two main phases in the island s tectonic metamorphic and magmatic evolution 1 an initial episode of extreme extension that exhumed hot lherzolites from the subcontinental lithospheric mantle and drove ultrahigh temperature metamorphism and melting of adjacent continental crust and 2 subsequent episodes of extensional detachment faulting and strike slip faulting that further exhumed granulites and mantle rocks across seram and ambon here we present the results of sixteen 40ar 39ar furnace step heating experiments on white mica biotite and phlogopite for a suite of twelve rocks that were targeted to further unravel seram s tectonic and metamorphic history despite a wide lithological and structural diversity among the samples there is a remarkable degree of correlation between the 40ar 39ar ages recorded by different rock types situated in different structural settings recording thermal events at 16 ma 5 7 ma 4 5 ma and 3 4 ma these frequently measured ages are defined in most instances by two or more 40ar 39ar ages that are identical within error at 16 ma a major kyanite grade metamorphic event affected the tehoru formation across western and central seram coincident with ultrahigh temperature metamorphism and melting of granulite facies rocks comprising the kobipoto complex and the intrusion of lamprophyres later at 5 7 ma kobipoto complex rocks were exhumed beneath extensional detachment faults on the kaibobo peninsula of western seram heating and shearing adjacent tehoru formation schists to form taunusa complex gneisses then at 4 5 ma 40ar 39ar ages record deformation within the kawa shear zone central seram and overprinting of detachment faults in western seram finally at 3 4 ma kobipoto complex migmatites were exhumed on ambon at the same time as deformation within the kawa shear zone and further overprinting of detachments in western seram these ages support there having been multiple synchronised episodes of high temperature extension and strike slip faulting interpreted to be the result of western seram having been ripped off from se sulawesi extended and dragged east by subduction rollback of the banda slab

geodynamic mechanism and classification of basins in the earth system abstract the sedimentary basin is a basic geological unit in the earth system its formation and evolution are controlled mainly by plate tectonics and geodynamics which have produced a variety of basin types the development and evolution of various basins depend not only on the tectonic effect of lithospheric plate but also on sublithospheric and earth surface actions basin classification schemes based on the theories of platform geosyncline or plate tectonics could neither include all basin types nor reflect the complex processes of basin formation and evolution from the viewpoint of earth system we proposed a new basin classification scheme based on geodynamic mechanism that is lithospheric plate sublithospheric and earth surface actions in our geodynamic classification we employed a series of geodynamic settings of basin formation and evolution including the lithospheric plate sublithospheric and earth surface environments the dynamic regimes of basin formation and evolution such as tectonic setting extension compression and shearing the thermal processes and gravity effects the various natures of basin basement and crustal types continental oceanic or transitional crust and the history of basin sedimentary filling and tectonic paleogeography successively as the controlling factors for basin classification this new geodynamic classification scheme highlights both the role of the lithosphere and the effects of the sublithospheric and the earth surface actions on controlling the basin formation and evolution the basic dynamic types of basin classification include the prototype basin forming under a single tectonic thermal or gravity regime and the superimposed basin as well as residual basin forming under multistage thermal and or tectonic regimes thus this classification scheme could provide an evolving understanding of lithosphere crust mantle interaction and geodynamic processes as well as of hydrocarbon accumulation and metallogenic mechanisms in sedimentary basins and would help in the synthetic exploration of various resources

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

late cenozoic palaeogeography of sulawesi indonesia abstract sulawesi has a remarkable biodiversity an unusually rich endemic fauna and is the largest island in wallacea just west of the wallace line alfred russel wallace himself suggested it could perhaps be the most remarkable island on the globe because of its peculiar fauna it was home to extinct fossil fauna such as dwarf proboscideans records significant pleistocene faunal turnover and evidence of early human occupation suggests an important role in hominid migration through the sunda sahul region information on neogene palaeogeography is essential for understanding biogeographic patterns biodiversity and faunal changes new palaeogeographic maps reflecting recent work on sulawesi s complex geology and changes in tectonic interpretations are presented for intervals from the early miocene to pleistocene at 20 15 10 8 6 5 4 3 2 and 1 ma additional maps illustrate the effects of glacially driven sea level change in the last 1 myr they are based on a field based investigation of sedimentary rocks in sulawesi accompanied by palaeontological petrological and heavy mineral studies and u pb dating of detrital zircons to date and determine depositional environments the new results have been supplemented by re evaluation of previous studies including reports from oil company wells and seismic lines igneous rocks provided ages indications of surface environment of eruptions and location of magmatic activity for most of the neogene from the early miocene sulawesi was a shallow marine area with a number of small islands surrounded by relatively deep marine areas deep inter arm bays began to form in the late miocene and the islands became larger the most significant palaeogeographic change began in the pliocene with an increase in the area and elevation of land accompanied by major subsidence of the inter arm bays the separate islands gradually coalesced in the pleistocene to form the distinctive k shaped island known today

white mica 40ar 39ar age spectra and the timing of multiple episodes of high p metamorphic mineral growth in the cycladic eclogite blueschist belt syros aegean sea greece research support providedby arc discovery projects dp0877274 anddp1201035 54 forster ackno wledges the support ofan australian research council arc australianresearch fellowship

forearc hyperextension dismembered the south tibetan ophiolites suprasubduction zone ophiolites are relics of oceanic upper plate forearcs and are typically preserved as discontinuous belts with discrete massifs along suture zones ophiolites usually contain an incomplete condensed section compared to average modern oceanic lithosphere the incompleteness and discontinuity of ophiolites are frequently attributed to dismemberment but tectonic causes remain poorly constrained here we show new paleomagnetic and field geological evidence for the preservation of extensional detachment faults that thinned and dismembered the south tibetan ophiolite belt during the early cretaceous similar to those documented in modern slow and ultraslow spreading ridges these detachments exhumed lithospheric mantle and subophiolitic melange to the seafloor which became unconformably covered by asia derived forearc strata we call this mechanism forearc hyperextension whereby widespread detachment faults accommodate upper plate extension above a subduction zone we propose that hyperextension is the key mechanism responsible for dismemberment of the south tibetan ophiolitic belt shortly after its magmatic accretion

early carboniferous metamorphism of the neoproterozoic south tien shan karakum basement new geochronological results from baisun and kyzylkum uzbekistan abstract paleozoic evolution of the western tien shan which is built up on the basement of the karakum continent is poorly constrained compared to the better investigated tien shan terranes along the margin of the tarim craton we present magmatic metamorphic and detrital zircon ages for the regionally metamorphosed baisun block and the metasediments comprising the karakum basement in the westernmost parts of the south tien shan terrane age spectra of detrital zircon from metasediments of the baisun metamorphic block and the western south tien shan show remarkable similarities over the vast area extending for ca 500 km and are characterized by major neoproterozoic peak at 1200 600 ma and smaller peaks at 2300 1700 and 2700 2400 ma the 570 540 ma ages of the youngest grains define late neoproterozoic ediacaran early cambrian maximum depositional ages of the metasediments comparison of the obtained age spectra with those published for the adjacent tien shan terranes indicate that the detrital zircon grains in the studied ediacaran sediments were derived from the southern precambrian continents of karakum and tarim while transport from the northern tien shan was limited the age of the barrovian metamorphism in the baisun block is constrained by ages of anatectic granites in the range 352 340 ma corresponding to early carboniferous these ages well match the 340 330 ma ages established for the adjacent lolabulak and garm metamorphic blocks based on the regional distribution of suture zones we suggest that during the carboniferous the relatively small tectonic blocks of the south gissar comprised an archipelago located between the larger continents of karakum and tarim and possibly connected with the paleotethys ocean the archipelago scenario can explain hot and rapid metamorphic and tectonic processes documented in the south gissar similar to the ongoing collision along the australia se asia junction

interaction of an antecedent fluvial system with early normal fault growth implications for syn rift stratigraphy western corinth rift greece continental overfilled conditions during rift initiation are conventionally explained as due to low creation of accommodation compared with sediment supply alternatively sediment supply can be relatively high from the onset of rifting due to an antecedent drainage system the alluvial lower group of the western plio pleistocene corinth rift is used to investigate the interac tion of fluvial sedimentation with early rifting this rift was obliquely super imposed on the hellenide mountain belt from which it inherited a significant palaeorelief detailed sedimentary logging and mapping of the well exposed syn rift succession document the facies distributions palaeocurrents and stratigraphic architecture magnetostratigraphy and bios tratigraphy are used to date and correlate the alluvial succession across and between fault blocks from 3 2 to 1 8 ma a transverse low sinuosity braided river system flowed north north east to east across east west striking active fault blocks 4 to 7 km in width deposits evolved downstream from coarse alluvial conglomerates to fine grained lacustrine deposits over 15 to 30 km the length scale of facies belts is much greater than and thus not directly controlled by the width of the fault blocks at its termination the distribu tive river system built small stacked deltas into a shallow lake margin the presence of a major antecedent drainage system is supported by i a single major sediment entry point ii persistence of a main channel belt axis iii downstream fining at the scale of the rift basin the zones of maximum sub sidence on individual faults are aligned with the persistent fluvial axis sug gesting that sediment supply influenced normal fault growth instead of low accommodation rate during the early rift phase this study proposes that facies progradation can be controlled by continuous and high sediment sup ply from antecedent rivers

surface deformation and slab mantle interaction during banda arc subduction rollback the reason for the spectacular curvature of the banda subduction zone is debated tomographic images and plate reconstructions reveal subduction of a single slab the ancient geometry of the australian plate as well as the interaction between the slab and the mantle caused the deformation of the slab the spectacularly curved banda arc comprises young oceanic crust1 2 enclosed by a volcanic inner arc outer arc islands and a trough parallel to the australian continental margin3 4 5 strong seismic activity in the upper mantle defines a folded surface6 7 for which there are two contrasting explanations deformation of a single slab5 8 or two separate slabs subducting from the north and south6 9 here we combine seismic tomography with the plate tectonic evolution of the region to infer that the banda arc results from subduction of a single slab our palaeogeographic reconstruction shows that a jurassic embayment which consisted of dense oceanic lithosphere enclosed by continental crust once existed within the australian plate banda subduction began about 15 million years ago when active java subduction tore eastwards into the embayment the present morphology of the subducting slab is only partially controlled by the shape of the embayment as the australian plate moved northward at a high speed of about 7 cm yr 1 the banda oceanic slab rolled back towards the south southeast accompanied by active delamination separating the crust from the denser mantle increasing resistance of the mantle to plate motion progressively folded the slab and caused strong deformation of the crust the banda arc represents an outstanding example of large scale deformation of the earth s crust in response to coupling between the crust slab and surrounding mantle

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

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

is high obliquity a plausible cause for neoproterozoic glaciations 1 the main features of the low latitude neoproterozoic glaciations remain the subject of controversial debates concerning possible triggers here we use an agcm coupled with a slab ocean to test one of the earliest and simplest explanation for tropical glaciations a higher obliquity of the earth s rotation axis we show that high obliquity may result in an extensive glaciation during the sturtian episode 750 ma due to the location of continental masses in the tropical areas but cannot produce a large glaciation in the case of mid to high latitude paleogeographies such as those thought to typify the varangian vendian episodes 620 580 ma

role of tectonic denudation in warping and uplift of low angle normal faults large displacement on a low angle normal fault results in isostatic uplift of the lower plate in response to tectonic denudation simple models of the denudation process predict warping of the lower plate into a broad antiform or antiform synform pair with axes perpendicular to the direction of extension the amount of warping is strongly influenced by initial fault geometry surface topography the amount of extension and the distribution of extension within the upper plate late stage processes that augment antiform growth include one sided denudation of the antiform reverse faulting due to concave upward flexure and wholesale detachment and reverse drag folding of the antiform antiformal uplifts now exhumed by erosion form mountain ranges in the southwestern united states where conditions were favorable for warping during mid tertiary crustal extension four major structural domains are apparent in transects across these uplifts and adjacent areas 1 unextended area 2 synformal upper plate 3 antiformal uplift and 4 wedge shaped upper plate each domain is separated from adjacent domains by the traces of a master low angle normal fault

neoproterozoic snowball earth dynamic sea ice over a quiescent ocean 1 low latitude sea level glacial deposits suggest the existence of snowball earth conditions in the neoproterozoic previous modeling studies have offered conflicting support for the snowball hypothesis we use a climate model of intermediate complexity including an ocean gcm and a sophisticated thermodynamic dynamic sea ice component to conduct a suite of experiments with different orbital paleogeographical configurations wind forcing and atmospheric co2 levels we show that depending on the orbital configuration and paleogeography snowball conditions prevail even with atmospheric co2 levels up to 1800 ppmv overall our modeling paradigm is consistent with the original snowball hypothesis in which an ice covered ocean surrounds a largely snow and ice free barren land with some coastal regions permitting the growth of thick glaciers

tectonic mode switches and the nature of orogenesis abstract the birth and death of many mountain belts occurs in lithosphere that over rides major subduction zones here the tectonic mode shortening versus extension can abruptly switch even during continuous and otherwise smooth convergence if the hinge line of the foundering slab rapidly retreats i e rolls back the foundering slab creates a gravitational potential well into which the orogen collapses this motion coupled with stress guides can pull the orogen apart a slowing of roll back or of hinge retreat means that the subduction flexure may subsequently begin to be pushed back or be pushed over by the advancing orogen the consequence of such changes in relative motion is that orogenic belts are affected by abrupt tectonic mode switches the change from push to pull leads to a sudden change from horizontal extension to horizontal shortening potentially throughout the entire mass of the orogenic lithosphere that over rides the subducting slab the sequencing of these tectonic mode switches affects the thermal evolution of the orogen and thus fundamentally determines the nature of orogenesis this insight led to us to our quite different views as to how orogens work it is evident that orogens affected by abrupt push pull mode switches are characterized by high pressure metamorphism whereas orogens affected by abrupt pull push mode switches are characterized by high temperature metamorphism magmatism and anatexis

neogene sutures in eastern indonesia five suture zones are described from the zone of collision between the eurasian indian australian and pacific philippine sea plates within the eastern indonesia region these are the molucca sorong sulawesi banda and borneo sutures each of these sutures has a relatively short history compared to most pre neogene orogenic belts but each preserves a record of major changes in tectonics including subduction polarity reversals elimination of volcanic arcs changing plate boundaries and important extension within an overall contractional setting rapid tectonic changes have occurred within periods of less than 5 ma many of these events although important would be overlooked in older orogenic belts because the age resolution required to identify them even when the evidence is preserved is simply not possible q 2000 elsevier science ltd all rights reserved

factors that inhibit snowball earth simulation 1 a coupled ocean atmosphere general circulation model with a thermodynamic sea ice model the fast ocean atmosphere model version 1 5 is used to investigate the factors that inhibit the simulation of global sea ice in the control experiment with reduced solar luminosity 93 of modern low atmospheric pco2 140 ppm and an idealized tropical continent the sea ice margin equilibrates at 27 latitude a series of experiments was completed to systematically test the influence of deep ocean circulation wind driven ocean circulation convective mixing sea ice treatment and radiative cloud forcing on the sea ice extent model results indicate that both wind driven circulation and cloud radiative forcing are critical factors that inhibit sea ice advance into the low latitudes the wind driven ocean circulation transports heat to the sea ice margin stabilizing the sea ice margin clouds yield a positive radiative forcing over ice warming the air overlying sea ice and decreasing sensible heat loss at the sea ice margin in the absence of either factor sea ice expands to the equator within 15 model years yielding a snowball earth we also find that intensification of the hadley circulation as sea ice enters the hadley domain promotes the climate instability that leads to global sea ice cover results from this study help explain the wide disparity in conditions necessary to simulate global ice cover in previous climate models of the neoproterozoic

earthquakes and tsunamis caused by low angle normal faulting in the banda sea indonesia as the world s largest archipelagic country in earth s most active tectonic region indonesia faces a substantial earthquake and tsunami threat understanding this threat is a challenge because of the complex tectonic environment the paucity of observed data and the limited historical record here we combine information from recent studies of the geology of indonesia s banda sea with global positioning system observations of crustal motion and an analysis of historical large earthquakes and tsunamis there we show that past destructive earthquakes were not caused by the supposed megathrust of the banda outer arc as previously thought but are due to a vast submarine normal fault system recently discovered along the banda inner arc instead of being generated by coseismic seafloor displacement we find the tsunamis were more likely caused by earthquake triggered submarine slumping along the fault s massive scarp the weber deep this would make the banda detachment representative not only as a modern analogue for terranes hyper extended by slab rollback but also for the generation of earthquakes and tsunamis by a submarine extensional fault system our findings suggest that low angle normal faults in the banda sea generate large earthquakes which in turn can generate tsunamis due to earthquake triggered slumping low angle normal faults in the banda sea have caused large earthquakes that indirectly generated tsunamis due to earthquake triggered submarine slumping according to an analysis of historical earthquake and tsunami events and gps observations

low angle normal faults and seismicity a review although large low angle normal faults in the continental crust are widely recognized doubts persist that they either initiate or slip at shallow dips 30 because 1 global compilations of normal fault focal mechanisms show only a small fraction of events with either nodal plane dipping less than 30 and 2 andersonian fault mechanics predict that normal faults dipping less than 30 cannot slip geological reconstructions thermochronology paleomagnetic studies and seismic reflection profiles mainly published in the last 5 years reinforce the view that active low angle normal faulting in the brittle crust is widespread underscoring the paradox of the seismicity data for dip slip faults large enough to break the entire brittle layer during earthquakes m w 6 5 consideration of their surface area and efficiency in accommodating extension as a function of dip suggests average recurrence intervals of earthquakes r tan assuming stress drop rigidity modulus and thickness of the seismogenic layer do not vary systematically with dip if the global distribution of fault dip normalized to total fault length is uniform the global recurrence of earthquakes as a function of dip is shown to be r tan sin this relationship predicts that the frequency of earthquakes with nodal planes dipping between 30 and 60 will exceed those with planes shallower than 30 by a factor of 10 in good agreement with continental seismicity assuming major normal faults dipping more than 60 are relatively uncommon revision of andersonian fault mechanics to include rotation of the stress axes with depth perhaps as a result of deep crustal shear against the brittle layer would explain both the common occurrence of low angle faults and the lack of large faults dipping more than 60 if correct this resolution of the paradox may indicate significant seismic hazard from large low angle normal faults

subduction in eastern indonesia how many slabs abstract seismicity associated with arc continent collision in eastern indonesia testifies to past north directed subduction of indian ocean lithosphere beneath the banda sea the complex patterns of deep seismicity have been cited as evidence for simultaneous south directed subduction at the northern margin of the sea but this interpretation has not been universally accepted recently available recomputations of hypocentre locations have provided increased resolution of eastern indonesian wadati benioff zones wbzs shallow to intermediate depth seismic activity around the banda arc appears to support models involving subduction of two separate and distinct lithospheric slabs but between 150 and 500 km the wbz has a continuous shoehorn shape this shape confirms the presence of subducted lithosphere beneath seram in the north as well as beneath timor in the south is incompatible with independent subduction of two unconnected plates and implies rapid eastwards retreat of the subduction trace across a now vanished northern spur of the indian ocean this roll back is unlikely to have been driven by local gravitational forces alone and may have been sustained by injection behind the banda slab of asthenospheric material escaping from the molucca sea arc arc collision

active tectonics of the eastern sunda and banda arcs the tectonics of the eastern sunda and banda arcs of eastern indonesia are inferred from the centroid depths seismic moments and fault plane solutions of 63 large earthquakes that occurred between 1962 and 1984 source parameters are estimated by inverting long period teleseismic p and sh waves earthquakes show that the collision of the australian continent with the banda arc shortens the upper plate beneath the forearc and back arc basin over the broad area between the timor and seram troughs along the eastern end of the sunda arc and along the southern banda arc earthquakes reveal that the arc and forearc respond to collision by shortening in the direction of convergence by elongating in the direction perpendicular to convergence and by thrusting over the back arc basin shallow thrust and strike slip earthquakes beneath the banda basin the back arc basin demonstrate that deformation within the back arc accommodates some of the northward motion of the australian continent the rate of north south shortening of the entire upper plate at the longitude of timor calculated from the seismic moments of the earthquakes over the 22 year period is roughly 20 of the predicted convergence rate between australia and southeast asia strike slip faulting within the banda basin results also in eastward motion of the banda arc with respect to western indonesia and australia eastward extrusion of the banda arc results in thrusting at the aru trough earthquakes due to thrusting of the back arc basin beneath the volcanic arc are too shallow to corroborate that the arc s polarity has reversed although the wetar back arc thrust zone at present has a high seismic slip rate earthquakes and their mechanisms provide evidence that the lithosphere of the weber basin a 7500 m deep forearc basin rests on the subducting lithosphere without intervening asthenosphere so that the weber basin subsides in response to sinking of the subducting lithosphere closure of the banda basin is geometrically incompatible with the australian plate subducting simultaneously beneath both the timor and seram troughs instead the bird s head which subducts beneath seram is decoupled from the australian plate in western new guinea and probably moves west or southwest with respect to australia in the eastern indonesian example strike slip faulting plays a major role in the evolution of the collision zone and clearly demonstrates the complexity in three dimensions of continental accretion and mountain building by arc continent collision

active aseismic creep on the alto tiberina low angle normal fault italy the existence of active low angle normal faults has been questioned because the standard theory of fault mechanics precludes normal faults from slipping at low

rain shadow development during the growth of mountain ranges an atmospheric dynamics perspective 1 an idealized atmospheric model is used to explore the links between climate and topography in the development of orographic rain shadows during orogenesis the atmospheric dynamics theory of density stratified fluid flow over topography is used to interpret the results the controlling nondimensional parameter is nh u where n is the brunt vaisala frequency a measure of atmospheric stability h is the terrain relief and u is the initial horizontal wind speed rain shadow development is found to be a nonlinear and nonunique function of both topography and atmospheric state indicating that geological records of orographic aridity cannot be interpreted in terms of relief alone when upstream topography exceeds nh u 1 during surface uplift downstream orographic precipitation vanishes and downstream orographic cloud mass decreases by as much as 90 upstream blocking of air flow can generate a forward projecting rain shadow in which a relatively low ridge nh u 1 may be decoupled from the atmospheric flow by a zone of flow stagnation extending upstream of the high terrain such an effect may occur if the valley separating the two ranges is narrower than the length scale of flow stagnation in the model configuration used here lateral widening of a relatively low nh u 1 range increases downstream cloud mass by up to a factor of 3 these results help to refine interpretations of climate tectonic interactions in shaping the geological record of the sierra nevada and andes

forearc extension and slow rollback of the calabrian arc from gps measurements 1 here we describe the horizontal velocities of continuous gps stations in the calabrian arc ca and surrounding regions the appropriate reference frame to evaluate the crustal motion of the ca is considered by assessing the internal deformation and the relative motion of the crustal blocks in the foreland of the apennines ionian maghrebides subduction system we propose that the motion of ca relative to the subducting ionian lower plate is most properly assessed by minimizing the gps velocities in apulia in this reference frame the significant 2 mm yr southeastward motion of the stations on the ionian flank of the ca shows that the arc is still moving towards the trench in agreement with the observations of active shortening in the ioanian wedge this southeastward migration is associated to 1 4 0 3 mm yr e w extension of the forearc in northern calabria comparable with the seismic strain averaged in the last 500 years the limited subaerial exposure decreases the resolution on locking of the subduction interface but the distribution and direction of crustal extension along the ca impose important constraints on geodynamic interpretations of the area

the 1674 ambon tsunami extreme run up caused by an earthquake triggered landslide we present an analysis of the oldest detailed account of tsunami run up in indonesia that of the 1674 ambon tsunami rumphius in waerachtigh verhael van de schuckelijcke aerdbebinge batavia dutch east indies 1675 at 100 m this is the largest run up height ever documented in indonesia and with over 2300 fatalities even in 1674 it ranks as one of indonesia s most deadly tsunami disasters we consider the plausible sources of earthquakes near ambon that could generate a large destructive tsunami including the seram megathrust the south seram thrust and faults local to ambon we conclude that the only explanation for the extreme run up observed on the north coast of amon is a tsunami generated by an earthquake triggered coastal landslide we use a two layer tsunami model to show that a submarine landslide with an approximate volume of 1 km3 offshore the area on ambon s northern coast between seith and hila where dramatic changes in coastal landscape were observed can explain the observed tsunami run up along the coast thus the 1674 ambon tsunami adds weight to the evidence from recent tsunamis including the 1992 flores 2018 palu and sunda strait tsunamis that landslides are an important source of tsunami hazard in indonesia

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin

gcm response to late precambrian 590 ma ice covered continents recent coupled energy balance ice sheet modeling studies indicate that ice covered continents can be simulated for the late precambrian with 6 solar constant reduction we examine the ocean mixed layer response to such an ice sheet with the genesis 2 general circulation model and co2 levels varying from 0 5 2 5 times present the ocean ices over completely at 0 5 1 0x present levels with the final phase of sea ice growth occurring within a single model year a qualitatively different 2 5x co2 solution is close to equilibrium and yields open water between 25 n and 25 s paleolatitude the prevailing wind patterns suggest that an equatorial pacific type circulation may have developed in part of the neoproterozoic ocean