Bela oceanic lithosphere assemblage and its relation to the Réunion hotspot

The Bela ophiolite of Pakistan contains a complete ophiolite-accretionary wedge-trench sequence emplaced onto the Indian continental margin during the northward drift of India-Seychelles over the active Réunion hotspot. A structurally higher ophiolite overlies an accretionary prism, which is thrust over a foreland basin. Shear-sense determinations in peridotite mylonites in the ophiolite footwall and imbrication structures in the underlying accretionary wedge indicate an ESE emplacement. Sedimentary rocks in the accretionary wedge indicate Aptian-Albian pillow lavas, initially deep water conditions, and increasing influence from the continent until the Maastrichtian. The ophiolite emplacement was predated and accompanied by Fe-tholeiitic and alkaline magmatism related to the Réunion hotspot and continuous incorporation of trench sediments into the accretionary wedge. ³⁹Ar/⁴⁰Ar dating shows that the ophiolite formed around 70 Ma. Intraoceanic subduction initiated between 70 and 65 Ma, obduction onto the Indian passive margin occurred during the formation of the Deccan traps at ≈ 66 Ma, and final thrusting onto the continental margin ended in the early Eocene (≈ 50 Ma). The ophiolite emplacement occurred during the counterclockwise separation of Madagascar and India-Seychelles which caused shortening and consumption of oceanic lithosphere between the African-Arabian and the Indian-Seychelles plates.     

Assessing the nature of tectonic contacts using fission-track thermochronology: an example from the Calabrian Arc, southern Italy

Fission-track thermochronology applied to the nappe pile of the Calabrian Arc of southern Italy, particularly within the continental basement rocks, has provided important new constraints on the nature of some of the tectonic contacts. In southern Calabria an important phase of lower Miocene crustal extension is indicated. In northern Calabria no Oligocene or younger extension is seen. Here, the emplacement of continental basement rocks with Alpine metamorphism over ophiolitic rocks with little or no metamorphism is constrained as a thrust of lower to middle Miocene age related to collision of the Calabrian Arc with the Adria plate margin. It is proposed that reduction in the plate convergence velocity during collision of a retreating subduction zone with a continental margin is, at least partly, an explanation for the onset of extension in southern Calabria during the Miocene.     

Variscan geodynamic evolution of the Carnic Alps (Austria/Italy)

The South-Alpine Carnic Alps are part of the southern flank of the European Variscides and display a continuous sedimentary record from Late Ordovician to Devonian times followed by Carboniferous S-directed nappe stacking and Late Carboniferous to Early Permian post-collisional collapse. The tectonometamorphic and sedimentary evolution of the Carnic Alps resembles a continuous process where pre- and syn-orogenic volcanism, syn-orogenic flysch sedimentation, deformation including nappe stacking, metamorphism and tectonic collapse shift in age from internal zones in the N towards external zones in the S. New structural, petrological and sedimentological data are presented concerning the tectonometamorphic history of the Carnic Alps. We distinguish three thrust sheets or tectonic nappes differing in their stratigraphic, sedimentological, deformational and metamorphic histories which were thrust over each other in Carboniferous times. Our data lead to a new geodynamic model showing an evolution from rifting or back-arc spreading in the Late Ordovician to the establishment of a mature passive continental margin in the Late Devonian/Early Carboniferous, flysch sedimentation in an active continental margin setting during the Visean/Namurian and finally collision during the Late Carboniferous between the northern margin of Gondwana and a microcontinent to the N.     

Oceanic mafic rocks in the Eastern Alps

The Eastern Alps in Austria have been interpreted as a pile of thrust sheets resulting from the collision of two continental masses. The only remains of the ocean-floor which may once have separated these continents could be the highly deformed greenschists, metasediments and serpentinites found in the lower thrust sheets. To test this hypothesis, a total of sixty mafic rocks from the Großglockner, Mooserboden, Fusch, Hochtor, Matrei Zone and Strobl localities have been analysed for the stable trace elements, Ti, Zr, Y, Nb and Cr, and the less stable elements K, Rb, and Sr. Visual and statistical comparison of the stable elements with known magma types reveals that five of the sample groups classify clearly as tholeiitic ocean-floor basalts, while one group, the Fusch locality, classifies as within-plate (probably ocean island) basalts. It is suggested that the tectonic units containing such rocks comprise a mélange of disrupted oceanic crust, upper mantle and seamounts, pelagic sediments and continental margin sediments. The rocks may have formed in a large ocean basin, rather than a marginal basin behind an island arc.     

Structure of the Pre-Paleozoic Formation of the Central Ural Uplift in the Northern and Subpolar Urals and Its Relation with Gold Production

The Central Ural uplift occupies the near-Vodorazdelnaya part of the Urals. It is composed of metaterrigenous and metavolcanogenic Riphean–Vendian formations. Distributed folds, which formed in several stages, and various tectonic faults are widespread. The study of these structures in the areas located in the Northern and Subpolar Urals showed their lateral and temporal variability, which was reflected in the difference in morphology and nature of faulting. In the Vodorazdelnaya area of the Northern Urals, as a result of thrust–fold deformations, a complex fold structure of the sequence was formed, subsequently broken by two submeridional subparallel faults into blocks. In the Khalmerya area of the Subpolar Urals, there are several tectonic blocks bounded by gently eastward dipping and overlapping tectonic blocks that form a duplex structure. This series of thrust structures created a complex cover structure contrasting in composition and degree of deformation. Later, a northeastern strike-slip fault zone arose. The orientation of early isoclinal folds in the rocks indicates pressure from the northeast, during the formation of tectonic scales and sheets in the Precambrian basement. Then this pressure occurred from the southeast and the Lower Paleozoic sediments were involved in the thrust process. Differences in the features of the formation of structures apparently depend on the morphology of the eastern margin of the East European platform and the change in the vector of displacement of the thrust sheet. The movement of the thrust sheets within the continental margin occurred along the main surface of the fault, with which the thrust structures are articulated at depth. At the final stages, extended strike-slip-upthrust zones were established, which affected the distribution of he gold mineralization.

     

Tectonic history of the ophiolitic rocks of the highland border fracture zone, Scotland: Stable isotope evidence from rock-fluid interactions during obduction

The mafic and ultramafic rocks of the Highland Border Fracture Zone are ophiolitic remnants of a pre-Grampian marginal basin that opened either within, or to the north of, the Dalradian sedimentary pile. Closure of the basin was achieved through a combination of northerly-directed subduction, and obduction of ophiolitic thrust-slices onto the basin's southern margin. During the early stages of obduction, young hot peridotite slabs were thrust over the cold upper surfaces of lower thrust sheets, producing a dynamothermal metamorphic sole. Serpentinisation of these peridotites, whilst they were still cooling, occurred in a near-surface position through the interaction of meteoric waters. Subsequently, the ophiolitic thrust-sheets, which comprise lizardite serpentinites, spilitic pillow lavas, and aureole rocks, were thrust over the uppermost Dalradian nappes which were themselves being expelled southwards, thereby accommodating basement shortening. Grampian regional metamorphism of the nappe pile and overlying Highland Border Suite ophiolitic thrust sheets, produced greenschist metaspilites from the spilitic pillow lavas, induced minor retrogression in the aureole rocks, and caused the lizardite in the serpentinites to be recrystallised and replaced by antigorite. The Highland Border Suite greenschist facies metamorphic fluids were D-enriched compared with low-grade Dalradian metamorphic waters, and may have been mixtures of the latter and D-rich dehydration fluids released from the mafic rocks during dynamothermal metamorphism. Brittle fracturing and shearing in the serpentinites were responses to late deformation at different crustal levels during the final stages of emplacement, which involved gravity-sliding as well as downbending of the Dalradian nappes and ophiolitic thrust-sheets against the elevated Midland Valley block.     

Evidence for Neotethys rooted within the Vardar suture zone from the Voras Massif, northernmost Greece

Three conflicting models are currently proposed for the location and tectonic setting of the Eurasian continental margin and adjacent Tethys ocean in the Balkan region during Mesozoic–Early Tertiary time. Model 1 places the Eurasian margin within the Rhodope zone relatively close to the Moesian platform. A Tethyan oceanic basin was located to the south bordering a large “Serbo-Pelagonian” microcontinent. Model 2 correlates an integral “Serbo-Pelagonian” continental unit with the Eurasian margin and locates the Tethys further southwest. Model 3 envisages the Pelagonian zone and the Serbo-Macedonian zone as conjugate continental units separated by a Tethyan ocean that was sutured in Early Tertiary time to create the Vardar zone of northern Greece and former Yugoslavia. These published alternatives are tested in this paper based on a study of the tectono-stratigraphy of a completely exposed transect located in the Voras Mountains of northernmost Greece. The outcrop extends across the Vardar zone, from the Pelagonian zone in the west to the Serbo-Macedonian zone in the east.Within the Voras Massif, six east-dipping imbricate thrust sheets are recognised. Of these, Units 1–4 correlate with the regional Pelagonian zone in the west (and related Almopias sub-zone). By contrast, Units 5–6 show a contrasting tectono-stratigraphy and correlate with the Paikon Massif and the Serbo-Macedonian zone to the east. These units form a stack of thrust sheets, with Unit 1 at the base and Unit 6 at the top. Unstacking these thrust sheets places ophiolitic units between the Pelagonian zone and the Serbo-Macedonian zone, as in Model 3. Additional implications are, first, that the Paikon Massif cannot be seen as a window of Pelagonian basement, as in Model 1, and, secondly, Jurassic andesitic volcanics of the Paikon Massif locally preserve a gneissose continental basement, ruling out a recently suggested origin as an intra-oceanic arc.We envisage that the Almopias (Vardar) ocean rifted in Triassic time, followed by seafloor spreading. The Almopias ocean was consumed beneath the Serbo-Macedonian margin in Jurassic time, generating subduction-related arc volcanism in the Paikon Massif and related units. Ophiolites were emplaced onto the Pelagonian margin in the west and covered by Late Jurassic (pre-Kimmeridgian) conglomerates. Other ophiolitic rocks formed within the Vardar zone (Ano Garefi ophiolite, Unit 4) in latest Jurassic–Early Cretaceous time and were not deformed until Early Tertiary time. The Vardar zone finally sutured in the Early Tertiary creating the present imbricate thrust structure of the Voras Mountains.     

Permian–Triassic amalgamation of Asia: Insights from Northeast China sutures and their place in the final collision of North China and Siberia

The Central Asia Orogenic Belt (CAOB) corresponds to the domain where Siberia and Mongolia were welded to North China. The eastern extension of the CAOB in Northeast China is disputed, since both suture location and timing are poorly documented. This paper reports for the first time the recognition of two suture zones in the southern part of Northeast China (Manchuria), between the Fushun Mishan and Yilan-Yitong faults. In the Jilin Province, west-directed thrust sheets involving successively, from west to east, passive continental margin rocks, metamorphic rocks and ophiolites, block-in-matrix formations and arc plutons indicate a Permian–Early Triassic collision. In the Liaoning Province, arc plutonism and top-to-the-north ductile shearing, coeval with the emplacement of an ophiolitic nappe, suggest a Palaeozoic collision. These two sutures are correlated with the Ondor Sum and Solonker sutures, described in Inner Mongolia. A new geodynamic model involving rifting and collision of the southern part of the Xilinhot Block with North China is proposed.     

Syn-thrust deformation across a transverse zone: the Grem–Vedra fault system (central Southern Alps, N Italy)

The lateral continuity of the E?CW trending thrust sheets developed within the Lower to Middle Triassic cover of the central Southern Alps (Orobic belt) is disturbed by the occurrence of several N?CS trending transverse zones, such as the poorly known Grem?CVedra Transverse Zone (GVTZ). The GVTZ developed during the emplacement of the up to six S-verging thrust sheets consisting of Lower to Middle Triassic units, occurring immediately south of the Orobic Anticlines. The transverse zone, active during thrust emplacement related to the early Alpine compressions which pre-date the Adamello intrusion, includes three major vertical shear zones, the Grem, Pezzel and Zuccone faults. The major structure of the transverse zone is the dextral Grem fault, forming a deep lateral ramp between thrust sheets 3 and 5. A similar evolution also occurred along the Zuccone and Pezzel faults, which show a left-lateral displacement of syn-thrust folds. The Grem fault was later reactivated as an oblique tear fault during the emplacement of the Orobic Anticlines, due to back-thrusting along out-of-sequence thrust surfaces (Clusone fault). Transpressional deformations along the fault zone are recorded by the rotation of major syn-thrust folds, which also suggest a horizontal offset close to 0.5?km. Records of the first stage of evolution of the Grem fault are better preserved along its northern segment, and structural relationships suggest that it propagated southward and downward in the growing thrust stack. The study of the meso and megascopic structures developed along the GVTZ constrains the evolution of the transverse zone, illustrating the complex deformational phenomena occurring in a transpressional regime. The GVTZ probably reflects the existence of pre-existing tectonic lineaments with a similar orientation. Evidence of pre-existing structures are not preserved in the exposed units, nevertheless the N?CS extensional fault systems that characterize the Norian to Jurassic rifting history of the Lombardian basin are valid candidates.     

Thermal history of Australian passive margin cover sequences accreted to Timor during Late Neogene arc–continent collision,Indonesia

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 Casanova Complex of the Northern Apennines: A mélange formed on a distal passive continental margin

The Cretaceous-Palaeocene Casanova Complex occurs in two thrust sheets of the eugeosynclinal Ligurids of the Northern Apennines. It is a sedimentary mélange with ophiolitic and quartzose turbidites or limestone-shale olistostrome (submarine debris flows) as matrix. Exotic blocks of ophiolite and granite, serpentinite breccias and lenticular ophiolitic breccias and olistostromes contribute to the mélange character of the complex. Deformational structures include soft-sediment slump folds (indicating a SW-dipping palaeoslope) and boudins, a gradational slumped top to the mélange, small-scale faults in chert blocks and deformation associated with the emplacement of the exotic slide blocks. The blocks were shed as rotational slides from submarine fault scarps and are surrounded by haloes of debris created by submarine weathering. The stacking pattern of the blocks, with the originally stratigraphically highest ophiolite lithologies lowest in the pile of blocks, is explained by a diverticulation model with progressively deeper erosion. Mechanical analysis shows that the blocks were stable when partly exposed resting on a soft sediment substratum. Criteria which distinguish the Casanova Complex from a tectonic mélange, and which may be of value in other mélanges, are discussed. Previous interpretations of the complex as a precursor olistostrome to northeastward nappe emplacement (the Bracco ridge model) are rejected. The mélange is believed to have formed on ocean crust as a result of turbidite and debris flow sedimentation, soft sediment deformation, block faulting, gravity sliding and submarine erosion at the distal edge of a uniformly SW-dipping continental margin.     

Cenozoic Vertical-Axis Rotations of the Hoh Xil Basin, Central–Northern Tibet

Understanding the Cenozoic vertical-axis rotation in the Tibetan Plateau is crucial for continental dynamic evolution. Paleomagnetic and rock magnetic investigations were carried out for the Oligocene and Miocene continental rocks of the Hoh Xil basin in order to better understand the tectonic rotations of central Tibet. The study area was located in the Tongtianhe area located in the southern part of the Hoh Xil basin and northern margin of the Tanggula thrust system in central-northern Tibet. A total of 160 independently oriented paleomagnetic samples were drilled from the Tongtianhe section for this study. The magnetic properties of magnetite and hematite have been recognized by measurements of magnetic susceptibility vs. temperature curves and unblocking temperatures. The mean directions of the Oligocene Yaxicuo Group in stratigraphic coordinates(Declination/Inclination = 354.9°/29.3°, k = 33.0, α_(95) = 13.5°, N =5 Sites) and of the Miocene Wudaoliang Group in stratigraphic coordinates(Declination/Inclination = 3.6°/36.4°, k = 161.0, α_(95) = 9.7°, N =3 Sites) pass reversal tests, indicating the primary nature of the characteristic magnetizations. Our results suggested that the sampled areas in the Tuotuohe depression of the Hoh Xil basin have undergone no paleomagnetically detectable rotations under single thrusting from the Tanggula thrust system. Our findings, together with constraints from other tectonic characteristics reported by previous paleomagnetic studies, suggest tectonic rotations in the Cuoredejia and Wudaoliang depressions of the Hoh Xil basin were affected by strike-slip faulting of the Fenghuo Shan-Nangqian thrust systems. A closer examination of geological data and different vertical-axis rotation magnitudes suggest the tectonic history of the Hoh Xil basin may be controlled by thrust and strike-slip faulting since the Eocene.     

Metamorphism of an Early Palaeozoic continental margin, western Baie Verte Peninsula, Newfoundland

Metamorphic mineral assemblages and textures from Early Palaeozoic continental margin rocks in north-western Newfoundland indicate that different structural levels have contrasting metamorphic histories. Rocks of the East Pond Metamorphic Suite, which represent the older, structurally lower level of the margin, experienced an early high-pressure–low-temperature stage of metamorphism (10–12 kbar minimum, 450–500°C) which produced eclogite in mafic dykes and phengite–garnet assemblages in pelites. This was overprinted by higher temperature–lower pressure amphibolite facies metamorphism (700–750°C, 7–9 kbar minimum) which produced complex symplectic textures in rocks of all compositions. Rocks of the Fleur de Lys Supergroup, which were deposited in the stratigraphically higher levels of the rifted margin, reached pressures of 7–8.5 kbar at about 450°C during the early stages of metamorphism, overprinted by assemblages which indicate maximum temperatures of 550–600°C at about 6.5 kbar. The metamorphic history of both units is interpreted to be the result of thermal relaxation following initial burial of a continental margin by overriding thrust sheets. Since there is no evidence that maximum pressures or temperatures within the Fleur de Lys Supergroup were ever as high as those reached in the East Pond Metamorphic Suite, these rocks may have followed parallel, 'nested' P–T–t paths, with the more deeply buried East Pond Metamorphic Suite subjected to greater thermal relaxation effects. Quantitative modelling of P–T–t paths is not possible with the present data, owing to both large uncertainties in P–T estimates, and in the time of metamorphism.     

Mechanisms of thrust faulting in the gran sasso chain, central apennines, italy

The Gran Sasso chain in Central Italy is made up of an imbricate stack of eight thrust sheets, which were emplaced over the Upper Miocene—Lower Pliocene Laga Flysch. The thrust sheets are numbered from 1 to 8 in order of their decreasing elevation in the tectonic stack, and their basal thrusts are numbered from T₁ to T₈, accordingly. On the basis of their different deformation features, the major thrust faults fall into three groups: (1) thrust faults marked by thick belts of incoherent gouges and breccia zones (T₁, T₂, T₃); (2) thrust faults characterized by a sharp plane which truncates folds that had developed in the footwall rocks (T₅, T₆); and (3) thrust faults truncating folds developed in both the hangingwall and footwall units, and bordered by foliated fault rocks (T₇). The deformation features observed for the different faults seem to vary because of two combined factors: (1) lithologic changes in the footwall and hangingwall units separated by the thrust faults; and (2) increasing amounts of deformation in the deepest portions of the imbricate stack. The upper thrust sheets (from 1 to 6) are characterized by massive calcareous and dolomitic rocks, they maintain a homoclinal setting and are truncated up-section by the cataclastic thrust faults. The lowermost thrust sheets (7 and 8) are characterized by a multilayer with competence contrasts, which undergoes shear-induced folding prior to the final emplacement of the thrust sheets. Bedding and axial planes of folds rotate progressively towards the T₅, T₆, T₇ and T₈ thrust boundaries, and are subsequently truncated by propagation of the brittle thrust faults. The maximum deformation is observed along the T₇ thrust fault, consistent with horizontal displacement that increases progressively from the uppermost to the lowermost thrust sheet in the tectonic stack. The axial planes of the folds developed in the hangingwall and footwall units are parallel to the T₇ thrust fault, and foliated fault rocks have developed. Field data and petrographic analysis indicate that cleavage fabrics in the fault rocks form by a combination of cataclasis, cataclastic flow and pressure-solution slip, associated with pervasive shearing along subtly distributed slip zones parallel to the T₇ thrust fault. The development of such fabrics at upper crustal levels creates easy-slip conditions in progressively thinner domains, which are regions of localized flow during the thrust sheet emplacement.     

Cretaceous–Tertiary tectonic inversion of the Cotiella Basin (southern Pyrenees,Spain)

The Cotiella Nappe includes one of the most important Mesozoic basins of the southern Pyrenees, which was subsequently inverted during the Tertiary compression. The Late Cretaceous Cotiella Basin is here interpreted as the western sector of the Cretaceous Cotiella-Bóixols basin (100᎜ km wide), located in the central part of the southern Pyrenees. The present-day complex structure of the Cotiella Nappe is the result of the inversion process, linked to the emplacement of basement thrust sheets of the Axial zone. In its western sector, the Cotiella Nappe consists of several superimposed thrust sheets, with complex geometry, becoming simpler towards the east, with a single thrust surface and smaller displacements. The Cotiella-Bóixols basin underwent strong subsidence during the Early Cretaceous at its eastern sector, and its depocentre migrated westward during the Late Cretaceous. The reconstruction of the sedimentary basin to the pre-compressional stage shows that during the Mesozoic the Cotiella-Bóixols basin was located to the south of a basement high, which later became the Pyrenean Axial Zone. From a balanced cross section, it can be inferred that the Cotiella, north-verging extensional system was connected with the north-Pyrenean rift by means of a 10-km deep horizontal detachment. The compressional Tertiary detachment within the upper crust was shallower than the extensional detachment, and individualised four basement thrust sheets, which form the Axial Zone antiform.     

Extensional deformation along the late Precambrian-Cambrian Baltoscandian passive margin: the Sarektjåkkå Nappe,Swedish Caledonides

The structural evolution of a part of the late Precambrian Baltoscandian passive margin just before the inception of seafloor spreading is described, recording the change from deformation by faulting to dominantly magmatic extension of the crust. The allochthon of the Scandinavian Caledonides contains the imbricated passive margin of continental Baltica overlain by various exotic terranes. The Sarektjåkkå Nappe in the Seve Nappe Complex, which contains the outer parts of Baltica's passive margin, consists of sedimentary rocks, occurring as screens between Vendian (573±74 Ma) diabase dykes. These dykes constitute 70–80% of the nappe and locally form sheeted dyke complexes. The Sarektjåkkå Nappe largely escaped penetrative Caledonian deformation and preserves igneous, metamorphic and structural elements that are linked to the evolution of a pre-Caledonian rift to a passive continental margin. Extensional deformation before dyke emplacement is recorded by normal faults, pull-apart structures and folds. Unconformities, dykes affected by brittle deformation, and fluidization of sediments during dyke emplacement indicate close relations between the deposition of sediments, extensional deformation and dyke emplacement. The Sarektjåkkå Nappe is compared with other parts of the Baltica's passive margin and its tectonic evolution is discussed.     

Rise and fall of the Eastern Great Indonesian arc recorded by the assembly, dispersion and accretion of the Banda Terrane, Timor

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.     

Zabyat Formation, Semail Nappe, Oman: sedimentation on to an emplacing ophiolite

ABSTRACT The pelagic sediments of the Semail Ophiolite are depositionally overlain by ophiolite-derived sediments of the Zabyat Formation, dominated by matrix-supported rudites, with subordinate arenites and lutites. The detritus was locally derived from the ophiolite, in a deep marine environment indicated by both underlying and overlying pelagic carbonates. The Zabyat rocks are restricted to fault zones in the ophiolite which were active during emplacement. They are interpreted as debris shed from the sub-vertical fault zones during the initial disruption of the Semail ocean floor, prior to the final emplacement on to the Arabian continental margin. This interpretation places constraints on possible mechanisms of ophiolite emplacement.     

Alpine geodynamic evolution of passive and active continental margin sequences in the Tauern Window (eastern Alps, Austria, Italy): a review

The Penninic oceanic sequence of the Glockner nappe and the foot-wall Penninic continental margin sequences exposed within the Tauern Window (eastern Alps) have been investigated in detail. Field data as well as structural and petrological data have been combined with data from the literature in order to constrain the geodynamic evolution of these units. Volcanic and sedimentary sequences document the evolution from a stable continent that was formed subsequent to the Variscan orogeny, to its disintegration associated with subsidence and rifting in the Triassic and Jurassic, the formation of the Glockner oceanic basin and its consumption during the Upper Cretaceous and the Paleogene. These units are incorporated into a nappe stack that was formed during the collision between a Penninic Zentralgneis block in the north and a southern Austroalpine block. The Venediger nappe and the Storz nappe are characterized by metamorphic Jurassic shelf deposits (Hochstegen group) and Cretaceous flysch sediments (Kaserer and Murtörl groups), the Eclogite Zone and the Rote Wand–Modereck nappe comprise Permian to Triassic clastic sequences (Wustkogel quartzite) and remnants of platform carbonates (Seidlwinkl group) as well as Jurassic volcanoclastic material and rift sediments (Brennkogel facies), covered by Cretaceous flyschoid sequences. Nappe stacking was contemporaneous to and postdated subduction-related (high-pressure) eclogite and blueschist facies metamorphism. Emplacement of the eclogite-bearing units of the Eclogite zone and the Glockner nappe onto Penninic continental units (Zentralgneis block) occurred subsequent to eclogite facies metamorphism. The Eclogite zone, a former extended continental margin, was subsequently overridden by a pile of basement-cover nappes (Rote Wand–Modereck nappe) along a ductile out-of-sequence thrust. Low-angle normal faults that have developed during the Jurassic extensional phase might have been inverted during nappe emplacement.     

Late Precambrian subduction and collision in the Al Amar—Idsas region, Arabian Shield, Kingdom of Saudi Arabia

Recent work on outer arcs and collision belts provides for the first time a possible model for evolution of part of the Arabian Shield. The thick volcanic, volcaniclastic and sedimentary succession of the Proterozoic Halaban Group in the east of the Shield is intruded by synto late tectonic plutons and resembles Cenozoic subduction-related magmatic areas. West of the Halaban Group, and separated from it by a major east-dipping thrust with associated ultrabasic rocks and carbonates, are folded chlorite—sericite metasediments of the Abt Schists, comparable to Cenozoic outer arc successions. West of and beneath the Abt Schists calcareous and arenaceous metasediments of the Ar-Ridaniyah Formation are analogous to Mesozoic—Cenozoic continental margin shelf facies of the subducting plate. Eastward subduction with magmatism (Halaban Group) and tectonic emplacement of ocean-floor sediments (Abt Schists) was followed by continental collision and eastward underthrusting by the Ar-Ridaniyah Group and cratonized central part of the Shield. Collision-related post-tectonic granites were emplaced during and following the collision.