Tectonics

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.

Brazilian Margin, discussing the main phases of subsidence and sedimentation and in particular, the structural styles and depositional megasequences of selected basins. The Mesozoic sedimentation along the Brazilian continental margin started with the breakup of Western Gondwana in the Late Jurassic/Early Cretaceous. The rifting of the southernmost part of South America Plate was heralded by the extrusion of flood basalts in the Paraná, Campos and Santos basins. The syn-rift phase is associated with synthetic and antithetic faults forming several half-grabens filled with fluvial-deltaic sediments of the Continental Megasequence. The Transitional Megasequence is characterized by evaporite deposition from the Santos towards the Sergipe/Alagoas Basin, and salt movements constitute one of the most important controls on stratigraphic and structural features, being responsible for several exploratory plays in deep water regions. The drift Marine Megasequence, presently bearing most of the hydrocarbon production and reserves, may be subdivided into a carbonate Restricted Marine Supersequence (Albian to Turonian) and a siliciclastic Open Marine Supersequence (Late Cretaceous to Quaternary). The interpretation of deep water depositional systems and the rift architecture at the transition from continental to oceanic crust constitute the major challenges for petroleum exploration in the next century.

An integrated study involving sedimentology, mineral chemistry and spectroscopy highlights a distinctive compositional evolution of Cretaceous glauconite within the Ukra Hill Member. Glauconite occurs at the top part of transgressive systems tract deposits built on a marine shelf. The concentration of glau-conite steadily increases towards the maximum flooding surface, maximizing around 50%, and sharply falls at the onset of progradation. Unlike most Phanerozoic examples, Ukra glauconite forms by the variable degree of replacement of quartz, feldspar and mica grains. XRD, FEG-SEM and spectroscopy of glauconite pellets indicate an 'evolved' stage of maturation. Mossbauer spectroscopy reflects a minor substitution of Al 3þ-Fe 3þ (total) in tetrahedral sites and significant substitution of the same in octahedral sites. A consistently high value of K 2 O as well as Fe 2 O 3 contradicts the two popular theories, 'layer lattice' and 'verdissement', and support replacement origin of glauconite in a high a Siþ and high a Kþ pore water environment. Incipiently formed glauconite records a marginal increase in K 2 O content accompanied by release of Al 2 O 3 and SiO 2 to form evolved glauconite pellets; those forming within quartz grains involve an addition of Fe 2 O 3 (total) content during maturation. The minimal increase in K 2 O content of incipiently formed glauconite, best exhibited by those formed within quartz grains is possibly related to stratigraphic condensation. Compositional evolution like this is exhibited by Precambrian glauconites involving abiotic substrates, but is unusual for the Phanerozoic. Original K 2 O and Fe 2 O 3 (total) content of glauconites is reduced around peripheries and fractures during diagenesis, adding to compositional variability.

Within the framework of the International Continental Drilling Program (ICDP) we propose a comprehensive initiative to drill the continental crust bordering modern and ancient convergent and collisional plate boundaries. These zones host the vast majority of modern megacities and industrial installations on Planet Earth, and at the same time are loci of major earthquakes , tsunamis, volcanic eruptions and other associated great natural threats to human life and to economies. In-depth understanding of dynamic Earthprocesses at convergent and collisional plate boundaries is not possible without scientific drilling embedded into integrated research programmes. The set of scientific questions identified here is rooted in the plate tec-tonic paradigm of a dynamic Earth. Proposed studies derived from these questions target on (1) the dynamics of active subduction and collision zones, with focus on the seismogenic zone at the plate interface, and the distribution of deformation and seismicity in general, (2) the role of mantle plumes in orogeny, (3) supra-subduction magmatism in arc systems, (4) the geological manifestation of deep subduction and exhumation of the lithosphere, and (5) aspects relating to continental birth and growth through Earth history. ICDP drilling in convergent and collisional plate margins faces unprecedented challenges regarding drilling technology, drilling depth and requirements for long-term monitoring of Earth processes in downhole observatories.

Archean, Paleoproterozoic, and Mesoproterozoic rocks, assemblages, and structures differ greatly both from each other and from modern ones, and lack evidence for subduction and seafloor spreading such as is widespread in Phanerozoic terrains. Most specialists nevertheless apply non-actualistic plate-tectonic explanations to the ancient terrains and do not consider alternatives. This report evaluates popular concepts with multidisciplinary information, and proposes options. The key is fractionation by ca. 4.45 Ga of the hot young Earth into core, severely depleted mantle, and thick mafic protocrust, followed by still-continuing re-enrichment of upper mantle from the top. This is opposite to the popular assumption that silicate Earth is still slowly and unidirectionally fractionating. The protocrust contained most material from which all subsequent crust was derived, either directly, or indirectly after downward recycling. Tonalite, trondhjemite, and granodiorite (TTG), dominant components of Archean crust, were derived mostly by partial melting of protocrust. Dense restitic protocrust delaminated and sank into hot, weak dunite mantle, which, displaced upward, enabled further partial melting of protocrust. Sinkers enriched the upper mantle, in part maintaining coherence as distinct dense rocks, and in part yielding melts that metasomatized depleted-mantle dunite to more pyroxenic and garnetiferous rocks. Not until ca. 3.6 Ga was TTG crust cool enough to allow mafic and ultramafic lavas, from both protocrust and re-enriched mantle, to erupt to the surface, and then to sag as synclinal keels between rising diapiric batholiths; simultaneously upper crust deformed ductily, then brittly, above slowly flowing hot lower TTG crust. Paleoproterozoic and Mesoproterozoic orogens appear to be largely ensialic, developed from very thick basin-filling sedimentary and volcanic rocks on thinned Archean or Paleoproterozoic crust and remaining mafic protocrust, above moderately re-enriched mantle. Subduction, and perhaps the continent/ocean lithospheric dichotomy, began ca. 850 Ma – although fully modern plate- tectonic processes began only in Ordovician time – and continued to enrich the cooling mantle in excess of partial melts that contributed to new crust. “ Plumes ” from deep mantle do not operate in the modern Earth and did not operate in Precambrian time.

The transition from mechanical thinning toward focused magmatic intrusion during continental rifting is poorly constrained; the tectonically active Main Ethiopian Rift (MER) provides an ideal study locale to address this issue. The presence of linear magmatic-tectonic belts in the relatively immature central MER may indicate that the transition from mechanical to magmatic rifting is more spatially distributed and temporally protracted than has previously been assumed. Here we examine lava geochemistry and vent distribution of a Pliocene-Quaternary linear magmatic chain along the western margin of the central MER-the Akaki Magmatic Zone. Our results show limited variability in parental magma that evolve in a complex polybaric fractionation system that has not changed significantly over the past 3 Ma. Our results suggest the following: (1) channeling of plume material and the localization of shear-or topography-induced porosity modulates melt intrusion into the continental lithosphere.

The largest earthquake in the Zagros Mountains struck the city of Azgeleh on the Iran-Iraq border on 12 November 2017. This M w 7.3 earthquake was followed by an intense seismic sequence. Implementing the double-difference earthquake location technique, we relocate 1069 events recorded by our local seismic network, deployed after the mainshock. The spatial distribution of the epicenters indicates linear alignments of the events nucleated along at least four notable clusters. The clusters are characterized by at least one significant earthquake, such as the Tazehabad earthquake of 25 August 2018 (M w 5.9) along a dense, east-west trending cluster and the Sarpol-e Zahab earthquake of 25 November 2018 (M w 6.3) along the cluster with a northeast-southwest trend. We use two-pass differential SAR interferometry (DInSAR) and Small BAseline Subset (SBAS) methods to study the coseismic permanent displacements of the Azgeleh, Tazehabad and Sarpol-e Zahab events as well as the one-year postseismic deformation field of the 2017-2018 seismic sequence, respectively. We use non-linear and linear optimization algorithms to derive the source geometry and the slip distribution along the fault planes. The inversion is conducted by introducing also seismological constraints, leading to the definition of a listric geometry for the Azgeleh mainshock rupture that accommodates the slip area at depth of 10-16 km along a sub-horizontal plane (dipping ~3 •) and a low-angle (~16 •) ramp. The thrust and dextral movements along this NNW-striking (~345 •) fault have triggered a tear fault responsible for the Tazehabad event ruptured an east-west trending (~267 •), north-dipping (~78 •) sinistral shear fault. We present the dextral slip distribution of the Sarpol-e Zahab event along a NE-striking (~34 •) fault, as a synthetic Riedel structure for the southern segment of the Khanaqin fault, dipping 63 • to the southeast. We find the postseismic deformation field associated with the seismic sequence is not confined only to the mainshock source (the Azgeleh fault), but also develops along the Tazehabad and Sarpol-e Zahab faults. We additionally propose afterslip along a duplex, flat-ramp-flat structure down-dip and up-dip of the Azgeleh coseismic slip area. The up-dip afterslip develops onto the shallow detachment (~3 •) at depth of ~8 km and the down-dip afterslip propagate onto the mid-crustal décollement level within the Pan-African basement. The Azgeleh, Tazehabad, Sarpol-e Zahab and Khanaqin faults mark the Lurestan Arc-Kirkuk Embayment sharp margin in the Northwest Zagros and play a key role in the lateral escape of the Lurestan Salient and vertical strain partitioning in the Zagros front.

1] The long-term erosional evolution of relief is revealed by low-temperature thermochronometric data, whereas geomorphic features give constraints on the short-term evolution. We discuss the topographic evolution of northeastern Corsica by fission track and (U-Th)/He dating of apatite, the provenance of Neogene alluvial sediments, an analysis of uplifted strath terraces, and the shape of river profiles. Cooling ages indicate high cooling rates of up to 40°C/Myr during the early-middle Miocene, when this region was affected by extensional tectonics. Cooling rates are less than 7.5°C/Myr from the middle Miocene to the present, when topographic perturbations are detected by variations in the source areas of middle-to-late Miocene alluvial sediments and by the presence of large-scale irregularities along modern river longitudinal profiles. We suggest that the contrast of slow long-term erosion rates and the high local relief in the present Corsican landscape require that the landscape be in a transient state in response to a recent tectonic event. Citation: Fellin, M. G., M. Zattin, V. Picotti, P. W. Reiners, and S. Nicolescu (2005), Relief evolution in northern Corsica (western Mediterranean): Constraints on uplift and erosion on long-term and short-term timescales,

Advanced modal analysis methods are integrated with seismic reconstructions, gravity/ magnetic, and well/core data, revealing the complex geo-history of Pangean organization, and its consequent tectonic break-up, mainly during the Cretaceous and Cenozoic 1,2. Sediment transport systems from orogenic Caledonian and Uralian terrains, as well as Fenno-Skandinavian shield areas, provide a wide variety of provenance signatures, as well clastic wedge basin fill sequences, recording the tectonic evolution of convergent margins creating the super-continent Pangea in this region. These sequences, are followed by rifting events related to the opening of the Arctic Ocean basins 3. Pronounced uplift and erosion episodes of Arctic Greenland-Norwegian continental margins also occur during these times of rifting. Such episodes are related to the lack of accommodation for Arctic sea-floor spreading rates, where the coupled continental margin drift rate is < ½ of the total ridge spreading rates, resulting in inversion displacement along pre-existing fault systems (inverse Beta motions). In more extreme cases, under-plating of the lithosphere, subduction and regional uplift can be realized over broad areas 4 , which would have significant implications for energy exploration in prospective basin areas, particularly where uplift/ erosion exceeds c. 1.5 km 5,6. These tectonically uplifted terrains may also contribute to the Earth's long-term climate shift from greenhouse to icehouse environmental conditions during the Cenozoic 7. The lack of accommodation for mainly North-South opening of the Arctic Ocean may be a global consequence of the predominant equatorial East-West spreading creating the Atlantic Ocean further South, including that of the Icelandic ridge system. This appears to be a common feature of Arctic continental margins, and possibly passive margins in general 8. Ultimately, this lack of accommodation may herald termination of the prevailing Wilson cycle 9 , where initiation of oceanic subduction below the uplifted continental margin followed by the transformation of passive continental margins into a convergent margin with thrust fault deformations, subduction, and volcanism, which begins the next super-continental cycle.

Noctis Labyrinthus (Mars) is characterized by many tectonic features, which represent brittle deformation of the crust. This tectonic setting was analysed by remote sensing of the Viking Mars Digital Image Model (MDIM) mosaic and Mars Orbiter Camera (MOC) global mosaic, in order to identify deformational events. The main features are normal faults producing horst-graben structures, strike-slip faults, and related en-echelon and pull-apart basins. Using the criterion of cross-cutting relationships and analysis of secondary structures, to infer sense of movement of faults, two deformational phases were identiÿed in the Noctis Labyrinthus area. The ÿrst, D1, located mainly in the northern part, is characterized by transtensional faults (Noachian). The second, D2, recorded in the southern part of the Noctis Labyrinthus by an orthorhombic extensional fault pattern along NNE and WNW trends, is related to the Valles Marineris formation (Late Noachian-Early Hesperian). A third tectonic event, D3, represented by the partly known dextral NW strike-slip faults cross-cutting the Valles Marineris Canyon System

The contribution of subducted carbonate sediments to the genesis of the Southwestern Colombian arc magmas was investigated using a comprehensive petrography and geochemical analysis, including determination of major and trace element contents and Sr, Nd, Hf and Pb isotope compositions. These data have been used to constrain the depth of decarbonation in the subducted slab, indicating that the decarbonation process continues into the sub-arc region, and ultimately becomes negligible in the rear arc. We propose on the basis of multi-isotope approach and mass balance calculations, that the most important mechanism to induce the slab decarbonation is the infiltration of chemically reactive aqueous fluids from the altered oceanic crust, which decreasingly metasomatize the mantle wedge, triggering the formation of isotopically different primary magmas from the volcanic front (VF) with relatively high 176 Hf/ 177 Hf, high 87 Sr/ 86 Sr, negative values of eNd and lower Pb isotopes compared to the rear arc (RA).

Recent studies of the past eastern Australian landscape from present-day longitudinal river profiles and from mantle flow models suggest that the interaction of plate motion with mantle convection accounts for the two phases of large-scale uplift of the region since 120 Ma. We coupled the dynamic topography predicted from one of these mantle flow models to a surface process model to study the evolution of the eastern Australian landscape since the Jurassic Period. We varied the rainfall regime, erodibility, sea level variations, dynamic topography magnitude, and elastic thickness across a series of experiments. The approach accounts for erosion and sedimentation and simulates catchment dynamics. Despite the relative simplicity of our model, the results provide insights on the fundamental links between dynamic topography and continental-scale drainage evolution. Based on temporal and spatial changes in longitudinal river profiles as well as erosion and deposition maps, we show that the motion of the Australian plate over the convecting mantle has resulted in significant reorganization of the eastern Australian drainage. The model predicts that the Murray river drained eastward between 150 and ∼120 Ma, and switched to westward draining due to the tilting of the Australian plate from ∼120 Ma. First order comparisons of eight modeled river profiles and of the catchment shape of modeled Murray-Darling Basin are in agreement with present-day observations. The predicted denudation of the eastern highlands is compatible with thermochronology data and sedimentation rates along the southern Australian margin are consistent with cumulative sediment thickness.

Accurately mapping plate boundary types and locations through time is essential for understanding the evolution of the plate-mantle system and the exchange of material between the solid Earth and surface environments. However, the complexity of the Earth system and the cryptic nature of the geological record make it difficult to discriminate tectonic environments through deep time. Here we present a new method for identifying tectonic paleo-environments on Earth through a data mining approach using global geochemical data. We first fingerprint a variety of present-day tectonic environments utilising up to 136 geochemical data attributes in any available combination. A total of 38301 geochemical analyses from basalts aged from 5e0 Ma together with a well-established plate reconstruction model are used to construct a suite of discriminatory models for the first order tectonic environments of subduction and mid-ocean ridge as distinct from intraplate hotspot oceanic environments, identifying 41, 35, and 39 key discriminatory geochemical attributes, respectively. After training and validation, our model is applied to a global geochemical database of 1547 basalt samples of unknown tectonic origin aged between 1000 e410 Ma, a relatively ill-constrained period of Earth's evolution following the breakup of the Rodinia supercontinent, producing 56 unique global tectonic environment predictions throughout the Neo-proterozoic and Early Paleozoic. Predictions are used to discriminate between three alternative published Rodinia configuration models, identifying the model demonstrating the closest spatio-temporal consistency with the basalt record, and emphasizing the importance of integrating geochemical data into plate reconstructions. Our approach offers an extensible framework for constructing full-plate, deep-time reconstructions capable of assimilating a broad range of geochemical and geological observations, enabling next generation Earth system models.

We report results from an investigation of the geologic processes controlling hydrothermal activity along the previously-unstudied southern Mid-Atlantic Ridge (3-7°S). Our study employed the NOC (UK) deep-tow sidescan sonar instrument, TOBI, in concert with the WHOI (USA) autonomous underwater vehicle, ABE, to collect information concerning hydrothermal plume distributions in the water column co-registered with geologic investigations of the underlying seafloor. Two areas of high-temperature hydrothermal venting were identified. The first was situated in a non-transform discontinuity (NTD) between two adjacent secondorder ridge-segments near 4°02′S, distant from any neovolcanic activity. This geologic setting is very similar to that of the ultramafic-hosted and tectonically-controlled Rainbow vent-site on the northern Mid-Atlantic Ridge. The second site was located at 4°48′S at the axial-summit centre of a second-order ridge-segment. There, high-temperature venting is hosted in an ∼ 18 km 2 area of young lava flows which in some cases are observed to have flowed over and engulfed pre-existing chemosynthetic vent-fauna. In both appearance and extent, these lava flows are directly reminiscent of those emplaced in Winter 2005−06 at the East Pacific Rise, 9°50′N and reference to global seismic catalogues reveals that a swarm of large (M 4.6−5.6) seismic events was centred on the 5°S segment over a ∼ 24 h period in late June 2002, perhaps indicating the precise timing of this volcanic eruptive episode. Temperature measurements at one of the vents found directly adjacent to the fresh lava flows at 5°S MAR (Turtle Pits) have subsequently revealed vent-fluids that are actively phase separating under conditions very close to the Critical Point for seawater, at ∼ 3000 m depth and 407°C: the hottest vent-fluids yet reported from anywhere along the global ridge crest.

1] The ranges of the Eastern Sierras Pampeanas are located >600 km east of the Andean Cordillera in central Argentina and have been interpreted to be a response to shortening related to flat-slab subduction of the Nazca plate. Uplift of the ranges has been broadly documented to occur during Neogene time, but many questions remain regarding the timing and style of deformation, and the subsurface structural configuration. In this study, we address these unknowns with observations at multiple scales, integrate our results into a tectonic model for the area, and discuss how our structural interpretation fits with more regional tectonic models. Our major findings are: (1) The range-bounding faults thrust late Proterozoic to Cambrian schist and gneiss over poorly dated Pliocene to Pleistocene alluvial strata. The timing of fault displacement and age of footwall strata suggest that deformation may have been active at least by Pliocene time.

A kinematic model comprising 14 rotating, elastic-plastic blocks is used to represent the modern deformation of eastern Tibet and neighboring regions. Block rotations, fault slip rates and permanent strain rates within the blocks are constrained by inverting GPS velocities, slip vector azimuths derived from earthquakes, and fault slip rates derived from geology. The calculated internal strain rates of blocks in eastern Tibet amounts to 10 to 30 × 10 −9 /yr, in contrast to relatively low rates (b5×10 −9 /yr) in adjacent blocks including the south China, Alxa and Thailand blocks. F-test statistics show that neither the internal strain rates nor the spins of the blocks can be neglected in describing the surface deformation of eastern Tibet. Furthermore, slip on the main faults verifies that the use of deformable blocks can also predict strain localization and strike-parallel variations in slip rates. In terms of east-southeast motion of the eastern Tibetan plateau relative to the Eurasian plate, the net relative velocity contributed by internal strain rates in the blocks amounts to~10 mm/yr, about half of that due to the faulting. In terms of N-S shortening of plateau, however, the internal strain rises to a first order factor west of 95°E, contributing approximately 10 mm/yr, nearly two times larger than that from faulting. The kinematics in eastern Tibet shows that different types of deformation, i.e., NW-SE shear and N-S compression, are taken up by faulting on major faults and distributed contraction, respectively.

T h e motion of the Somalia plate relative t o the Nubia (Africa), Arabia and Antarctica platcs is re-evaluated using a new inversion method based o n a Monte Carlo technique and a least absolute value misfit criterion. A subset of the N U V E L 1 data set, with additional data along the Levant Fault and in the Red Sea is used. T h e results confirm that the motion of Arabia with respect to Africa is significantly different from the motion relative t o Somalia. It is further shown that the data along the SW Indian Ridge are compatible with a pole of relative motion between Africa and Somalia located close t o the hypothetical diffuse triple junction between the ridge and thc East African Rift. T h e resulting Africa-Somalia motion is then compatible with the geological structures and seismological data along the East African Rift system. Assuming a separate Somalia plate thus solves kinematic and geological problems around the Afar triple junction and along the East African Rift.

Although most data suggest that the India–Eurasia continental collision began approx 45–55 Myr ago, the architecture of the Himalayan–Tibetan orogen is dominated by deformational structures developed in the Neogene period (&lt; 23 Myr ago). The stratigraphic record and thermochronometric data indicate that erosion of the Himalaya intensified as this constructional phase began and reached a peak around 15 Myr ago. It remained high until approx 10.5 Myr ago and subsequently slowed gradually to approx 3.5 Myr ago, but then ...

The northeast trending Kapuskasing uplift transects the east-west belts of the central Superior Province over a distance of some 500 kin. Granulite to upper amphibolite facies rocks of the uplift form three distinct geological-geophysical entities: from south to north, the Chapleau, Groundhog River, and Fraserdale-Moosonee blocks. Uplift of the granulites along a moderately northwest dipping crustal-scale thrust fault is attributed to an early Proterozoic compressional event. Maior northeast-striking faults that bound the Kapuskasing zone on the west were examined by modelling of geophysical anomalies to determine dip and by geobarometry of garnetorthopyroxene-plagioclase-quartz assemblages to determine vertical displacement. Granulites in the Kapuskasing zone have 7-to 9-kbar signatures whereas those in the Quetico belt to the west indicate metamorphic pressure of 4-6 kbar. Individual calibrations of the barometer yield consistent pressure differences of 2-3 kbar, suggesting 7-10 km of west-sidedown movement on the faults. Modelling of gravity and aeromagnetic gradients indicates westerly dips of 60ø-65 ø , with west-side-down offset of up to 14 kin. These maior normal faults probably formed as collapse structures in response to crustal thickening which occurred Copyright 1986 by the American Geophysical Union. Paper number 6T023•. 0278-7•07/86/006T-023•$10.00 during the preceding compressional uplift stage. Differences in the configuration of individual blocks of the Kapuskasing zone can be related to variable fault slip and intersection angles between normal and reverse faults. Thus the Groundhog River and southern Fraserdale-Moosonee blocks are perched thrust tips analogous to the Sangre de Cristo Range of the Laramide uplift province, whereas the southern Chapleau block is a tilted slab with similar configuration to the Laramide Wind River Range. Pop-up geometry deduced for the northern Fraserdale-Moosonee block resembles the structure of the Laramide Uinta Mountains. A normal fault crosses the surface trace of the basal thrust fault between the Groundhog River and Fraserdale-Moosonee blocks and causes a 65-km "gap" without granulites. Regions of high-grade metamorphic rocks are commonly interpreted as uplifted portions of the deep crust. With the advent of mineralogic geobarometry, it is possible to quantify the amount of uplift and thus provide constraints on large-scale crustal structure. Granulite terranes can be classified as massif-type or tectonic slices (Newton and Perkins, 1982). Although both are characterized by metamorphic pressures of the order of $ + 1 kbar, with a few notable exceptions, the size and mechanisms of emplacement in the 554 Percival and McGrath: Kapuskasing Uplift Crustal Structure Hu ds o n Boy 60 ø 56 ø 57• ø Post -Archeon Wabigoon '•ca c OVer SUperior Province rnetavolcanic. Plutonic belt B•li rn e tas e dirn •'•• P lutonic b;•ary -0 toc krn 96 ø 76 ø 92 ø 88 ø 84 ø 80 ø Pig. 1. Location of the Kapuskasing uplift (KU) with respect to major features of the Canadian Shield, including the Kenyon structure (KS) and Winisk River fault (WRF). west-east transect in the southern part of the uplift, the pressure of final mineral equilibration increases from 2-3 kbar in low-grade supracrustal rocks of the Michipicoten belt (Studemeister, 1983), through amphibolite facies gneiss, to greater than 8 kbar in the Kapuskasing zone (Percival, 1983). In this paper, "Kapuskasing zone" refers to the linear NNE belt of geophysical anomalies and granulites, whereas "Kapuskasing uplift" is the low-to high-grade metamorphic transition (Figures 1 and 2). Exposure is rare in the northern part of the uplift, where the Kapuskasing zone crosses the Quetico metasedimentary gneiss belt (Bennett et al., 1967). In a west-east transect, metamorphic grade increases within the Quetico belt, from amphibolite facies in migmatitic paragneiss through a 90-kin-long zone of hypersthene-bearing paragneiss (Percival, 1985). The Foxville and Kineras faults separate the Quetico belt from biotite-poor granulites of the Kapuskasing zone to the east. The Lepage fault separates rocks of the Quetico belt from those of the Val Rita block, to the southeast, which include local granulite occurrences.

The Junggar terrane in China's Xinjiang Province sits adjacent to the Siberian craton and Kazakhstan block. A
nearly 100-m thick series of high-Mg lava flows is found in a Devonian arc in the Junggar terrane. The highly
porphyritic high-Mg lavas are stratigraphically in the lower part of the Middle Devonian Beitashan
Formation, and are overlain by basalts and andesites. Based on the chemistry and phenocryst contents, the
high-Mg lavas are classified into picrites and ankaramites. The former are characterized by a large amount of
olivine phenocrysts (Fo 79–82) with minor clinopyroxene (En44–50Fs1–10Wo44–48) and rare chrome spinel
with Cr# (Cr/Cr +Al) values between 0.63 and 0.86, whereas clinopyroxene phenocrysts are dominant in
ankaramite. The groundmass in the picrites and ankaramites consists of plagioclase, clinopyroxene, and Timagnetite.
Glass is not preserved, but minor metal sulfides are present. Based on olivine-melt equilibrium,
the primitive magmas had approximately 9 wt.% MgO, and the high-Mg lavas contain accumulated olivine
(picrites) and clinopyroxene + olivine (ankaramites). All lavas have similar primitive mantle normalized trace
element patterns, characterized by negative Nb, Ta and Ti anomalies, as typical for island arc volcanic rocks.
These relationships suggest that the rock suites are co-magmatic. The Zr/Nb ratios (23–66) of the picrites and
basalts resemble MORBs (10–66), suggesting MORB-like sources for the picrites. The picritic rocks have
slightly LREE-enriched patterns with (La/Yb)n ranging from 1.6 to 3.5 and (La/Sm)n from 1.2 to 2.1. In contrast,
basaltic rocks have flat to slightly LREE-enriched patterns with (La/Yb)n ranging from 1.2 to 5.7 and (La/Sm)n
from 0.8 to 2.5, whereas andesitic rocks have modestly LREE-enriched patterns with (La/Yb)n ranging from
2.8 to 9.1 and (La/Sm)n from 1.7 to 2.9. The REE patterns for all rocks do not exhibit Eu anomalies. The rocks
have similar (87Sr/86Sr)t (0.7033–0.7043, t= 385 Ma) and εNd(t) values (6.4–7.3), overlapping with the present
day island arc field. Consequently, primary magmas were most likely generated in N-MORB-type mantle,
which was modified by the addition of a fluid component derived from altered subducted oceanic crust as
indicated by elevated Sr/Nd and low Th/Yb ratios. REE modelling suggests that the primary magmas were
derived from garnet–spinel transition zone mantle.

1] The Tonga arc and associated Lau basin exhibit many geologically important processes that link subduction and mantle flow with plate separation and crustal production. We create seismic tomograms of the Tonga-Lau region by jointly inverting for Vp and Vp/Vs structure using data from the LABATTS ocean bottom seismograph experiment and several island deployments to better constrain dynamic processes in the mantle wedge. Jointly using P and S data can help distinguish between the various mechanisms responsible for seismic velocity anomalies such as temperature and the presence of melt and/ or volatiles. Because high attenuation in the wedge limits the S wave data set, we focus on 2-D inversions beneath the linear OBS array where resolution is best and also parameterize the solution in terms of the Vp/ Vs ratio. As expected, the subducting slab has fast Vp and Vs and a low Vp/Vs ratio, consistent with the cold downgoing plate. The Central Lau Spreading Center (CLSC) exhibits stronger anomalies in Vp/Vs than in Vp, with the anomalies larger than would be predicted purely by temperature variations. The CLSC anomaly extends >100 km to the west of the axis, suggesting a broad region of melt production driven by passive upwelling from plate separation rather than active upwelling mechanisms. The anomaly is asymmetric about the axis, suggesting that slab-induced corner flow possibly influences mantle dynamics several hundred kilometers away from the arc. There is a strong anomaly beneath the volcanic arc that gradually deepens as it trends toward the back arc, likely outlining a hydrated region of melt production that feeds the volcanic front. Hydration possibly continues throughout the wedge to at least 400 km depth. The Lau ridge exhibits a thicker lithosphere relative to the rest of the Basin, while the Fiji platform likely has a thinner lithosphere than the Lau Ridge from more recent extension. There is also a reasonable likelihood of a small degree of partial melt in the uppermost mantle beneath the platform.

Nine separate Cambrian to Carboniferous terranes are recognized in West Junggar, northwest China. They were amalgamated as part of the Central Asian Orogenic Belt which records accretion of continental, island-arc and oceanic terranes to Archaean-Proterozoic continental nuclei. Tangbale, Kekesayi, Ebinur and Mayila terranes (Cambrian-Silurian) evolved in intra-oceanic settings and docked, along a series of north-dipping subduction zones, on to the Laba terrane to their south. This southern continent was contiguous with lithosphere of the Kulumudi Ocean to the north. Devonian subduction on the northern edge of this ocean resulted in formation of a continental arc (Toli terrane) and accretionary complex (Kulumudi terrane). The Karamay terrane formed as an accretionary complex during the Carboniferous. The ophiolitic Sartuohai terrane was emplaced as melange between Kulumudi and Karamay terranes during the Late Carboniferous. Subduction migrated southward, continuing beneath these terranes, resulting in the intrusion of I-type granites into the Toli, Kulumudi, Sartuohai and Karamay terranes. These granites are closely associated with epithermal and porphyry-style gold mineralization. Composite terranes either side of the Kulumudi Ocean collided in the Late Carboniferous, marking the final consolidation of Central Asia. Collision was accompanied by anorogenic granite and diabase dyke intrusion, followed by widespread latest Carboniferous to Permian extension, and subsequently the formation of the Junggar Basin. West Junggar has been further disrupted by Cenozoic strike-slip faulting along Junggar and Dalabute faults.

We combine radiometric ages and geomorphologic investigations to quantify the relief creation of well preserved volcanic surfaces, applied to the volcanoes of southern Basse-Terre (Guadeloupe, Lesser Antilles Arc). The last 650 ka volcanic evolution of this island has been modeled using ten main stages constrained by K-Ar ages previously obtained on lava flows and domes from the volcanic massifs of the Axial Chain (1000-435 ka) and from the Grande Découverte Volcanic Complex (250 ka-present). Based on the construction of a 250,000-point database inferred from the analysis of the Guadeloupe Digital Elevation Model, 3D reconstructions of the successive volcanic stage landforms were calculated and the correlated geochronological maps drawn using ArcGIS software. Volumes and rates of construction were computed for each time span separating these ten stages. The average construction rates calculated here are 2.4 ± 0.3 × 10 −4 km 3 /yr for the last million years, 0.9 ± 0.3 × 10 −4 km 3 /yr for the last 100 ka, and 0.9 ± 0.2 × 10 −4 km 3 /yr for the last 15 ka. Although Basse-Terre volcanism is characterized by a marked dominance of effusive products, our estimates should be considered as minimum values because the material that went into the sea during explosive events was not taken into account. However, we note that a relatively high construction rate of 4.5 ± 1.3 × 10 −4 km 3 /yr has been obtained for the Icaques volcano, which was emplaced during the 630-600 ka time interval, within the depression formed by the first large-scale flank collapse having affected southern Basse-Terre. The sudden release of the lithostatic load induced by this mass-wasting event could explain this value, which is significantly higher than the average value of 0.8 ± 0.1 × 10 −4 km 3 /yr obtained for the last 650 ka. Finally, the comparison with other analogous volcanic massifs from islands and continental arcs points to a relatively low magmatic production for southern Basse-Terre, which could be tentatively related to the relatively slow subduction rate of the Atlantic plate.

A high-temperature shear zone, Toijem shear zone, with a top-to-the-SW sense of shear affects the core of the Higher Himalayan Crystallines (HHC) in western Nepal. The shear zone developed during the decompression, in the sillimanite stability field, of rocks that previously underwent relatively high-pressure metamorphism deformed under the kyanite stability field. PT conditions indicate that the footwall experienced higher pressure (∼9 kbar) than the hanging wall (∼7 kbar) and similar temperatures (675°-700°C). Monazite growth constrains the initial activity of the shear zone at 25.8 ± 0.3 Ma, before the onset of the Main Central Thrust zone, whereas the late intrusion of a crosscutting granitic dike at 17 ± 0.2 Ma limits its final activity. Monazites in kyanite-bearing gneisses from the footwall record prograde metamorphism in the HHC from ∼43 to 33 Ma. The new data confirm that exhumation of the HHC started earlier in western Nepal than in other portions of the belt and before the activity of both the South Tibetan Detachment System (STDS) and Main Central Thrust (MCT) zones. As a consequence, western Nepal represents a key area where the channel-flow-driven mechanism of exhumation, supposed to be active from Bhutan to central-eastern Nepal, does terminate. In this area, exhumation of crystalline units occurred by foreland propagation of ductile and, subsequently, brittle deformation.

This study describes the seismo-tectonic evolution of Cameroon. It is noticed that seismic activity is largely related to the Cameroon volcanic line (CVL) and many of the tectonic phenomena follow the previous structural lines. Although the area is that of a relatively low seismicity, the effects of a given earthquake could be considerable. This study combines seismic records, from 1952 to 2002 and from 2005 to 2007, with the integration of existing structural information to better define the seismogenic zones. An important identified cluster of epicenters in S-W defines the first seismic source region where events' characteristics show a weak seismicity related to volcanic activity. The second seismogenic zone, in the north of Mount Cameroon volcano, illustrates the activity of Central Cameroon Shear Zone (CCSZ) faults; its seismicity is considered weak to moderate with maximum magnitude recorded which is 5.1 Mb. The area of " Sanaga Shear Zone " (SSZ) constitutes the third seismic source region with moderate seismicity in which maximum magnitude recorded is 5.8 Mb; Depth of its faults segments is evaluated at 33 km. The fourth Source Region follows the North boundary of Congo Craton; a characteristic event with magnitude of 6 M allows evaluating fault depth at 33 km. Also three zones define crustal structure: the South Domain with thick crust, the Center Domain characterized by thin crust, active tectonic and volcanic structures and the north domain with shallow Moho.

The Texas Orocline, with a half wavelength of ~ 120 km, is the largest and most obvious orocline in the southern New England Orogen and is clearly recognised in geological maps and geophysical images. In the area of the orocline, there is a major unconformity between Devonian–Carboniferous metasedimentary rocks (Texas beds) and the overlying Early Permian rift-related basins. Detailed structural mapping shows that units both above and below the unconformity are folded around the orocline, indicating that at least part of the oroclinal deformation has occurred after the deposition of the Early Permian rocks. In addition, Early Permian (298–290 Ma) granitoids are aligned parallel to the oroclinal structure, further indicating that deformation partly occurred during or after the Early Permian. Pre-oroclinal isoclinal folds (F1) and related axial plane cleavage (S1) are well developed in the Texas beds and are curved around the oroclinal structure. Syn-oroclinal structures are characterised by minor kink folds and disharmonic folding (F2) in the core of the orocline. A later phase of kink folding corresponding to a ~ N–S shortening direction does not seem to be related to the orocline, and is interpreted as post-oroclinal deformation. A secondary penetrative fabric parallel to the axial plane of the orocline was not observed, indicating low contractional shortening across the orocline (< 30%). We demonstrate that the observed strain is too low to account for oroclinal bending during dextral transpression, as previously proposed. We suggest an alternative model involving an initial curved structure, probably related to subduction rollback or a pre-existing curvature in the palaeomargin of eastern Australia, which was amplified by dextral transpression and subsequent E–W contraction.

The South East Sayan area, W of the Lake Baikal is subjected to a very complex tectonic setting where the extensional stress field of the Baikal Rift System meets the compressional stress field generated by the India-Asia collision further south. Using satellite images, aerial photographs, SRTM DEM, field mapping of geomorphological structures, and published neotectonics and geological data we show that most of the relief in the SE Sayan initiated during Late Pliocene-Pleistocene through compressive reactivation of inherited structures. By Late Quaternary, clockwise rotation of the compressive field generated strike-slip faulting and local, secondary extension still within a general compressional stress field. We demonstrate that the formation of the small-scale extensional basins within the East Sayan range is not linked to general the extension in the Baikal Rift System nor to a possible asthenospheric plume acting at the base of the crust but rather to the rotation of small rigid tectonic blocks driven by the compression.

New 40 Ar/ 39 Ar, apatite fission track and (UeTh)/He data from the late Cretaceous indenting and buttressing margins of Ecuador have been combined with previous thermochronological studies to constrain the timing of syn-and post-accretionary tectonic events in the Ecuadorian Andes to within AE1 Ma. Our interpretations are more accurate than previous hypotheses because i) they are more sensitive to lower temperatures (<60 C), ii) we directly compare data obtained from in-situ and detrital rocks, and iii) they are constrained by recently published palaeomagnetic, stratigraphic and geochronological data. The response of the buttressing Ecuadorian margin to the collision of the Caribbean Plateau and its overlying arc was diachronous. Exhumation occurred as an immediate response to collision at w75 Ma, south of S1 30 0 , whereas the northern region started to exhume at w65 Ma, suggesting that accretion may have been oblique. Elevated cooling and exhumation rates within specific massifs dispersed along the entire length of the Ecuadorian cordilleras, during 43e30 and 25e18 Ma, are attributed to i) an increase in convergence rates between the Farallon and South American plates during 42e37 Ma, and an increase in spreading rates in the southern Atlantic ocean, and ii) a change in the vector of the subducting plate, which changed from ESE to E at 25 Ma in response to fragmentation of the Farallon Plate. Previous suggestions that Eocene reactivation of the buttressing margin were driven by collision of the Macuchi Arc are shown to be incorrect. 40 Ar/ 39 Ar, zircon fission track, and apatite fission track and (UeTh)/He analyses from the Eastern Cordillera north of S1 30 0 reveal well defined periods of rapid cooling and exhumation at 15 Ma, 9e7 Ma and 5.5e0 Ma. Apatite (UeTh)/He data reveals late Miocene-Recent cooling and exhumation ( 1.3 km) of the southern Eastern Cordillera by a lower quantity than that experienced to the north (!3.5 km). These distinguishable differences in cooling and exhumation are attributed to the collision of the Carnegie Ridge with the northern SOAM Plate at 15 Ma, and the subsequent subduction of high topography along the ridge at w5 Ma, which reactivated the serpentinised Campanian suture via dextral transcurrent displacement.

Using data from major earthquakes including the 9.1 magnitude earthquake that took place in Japan, on 11.03.2011, near the coast of Honshu, we calculated the dispersion curves for Love waves using data recorded at several stations located diversly in Romania. We processed the seismograms recorded at the broadband seismic stations. Even though results obtained are rather qualitative and not quantitative, we obtained some information about the depth of the Moho discontinuity, as well as the crustal structure, which is important especially since this kind of research has never been performed in Romania; the uncertainity comes from the fact that there is always a little ambiguity in the process of wave inversion, as well as in the process of interpretation.

Many authors have written and drawn that Sumatra is a homogeneous continental segment because it was constructed by continental blocks derived from Gondwana in different time and periods since initiation of Sundaland in the Triassic. There is an idea to suggest that Sumatra is fully recognized as a continental margin of Sundaland, while another idea draws that Sumatra consists of Sibumasu, West Sumatra Block and continental crust accreted onto Sundaland. However, both ideas have shown that Sumatra is composed of continental blocks. Geochemical signatures of Pasaman volcanic, collected from West Sumatra, using Ta/Yb versus Th/Yb discriminant diagram indicate that the rocks are derived from two different tectonic settings, not only from active continental margin (ACM) but also from oceanic arc tectonic environments. The discrimination becomes more clear and explicit in Yb (ppm) versus Th/Ta diagram where the ACM-derived rocks have Th/Ta ratio between 6-20 while the arc-derived samples show the ratio greater than 20. Identification of the tectonic setting origin of the volcanic can also be done using spider diagrams of selected trace elements, but it is not possible based on spider diagrams of REE. The geochemical signatures of Pasaman volcanic give evidence that Sumatra actually is not a homogenous segment of Gondwana-derived continental blocks, but consists of two different segments including ACM and arc tectonic settings. These evidences strengthen previous studies results in Lampung, Bengkulu and Central Sumatra. ABSTRAK Banyak penulis yang telah menulis dan menggambarkan bahwa Sumatera adalah sebuah segmen benua yang homogen, karena ia disusun oleh sejumlah blok bersifat benua yang berasal dari Gondwana dalam waktu dan periode yang berbeda-beda sejak pembentukan Sundaland pada Zaman Trias. Terdapat pemikiran yang menganggap bahwa Sumatera sepenuhnya dikenali sebagai tepian benua dari Sundaland, sementara itu pendapat lain menggambarkan bahwa Sumatera terdiri dari Sibumasu, Blok Sumatera Barat dan kerak benua yang didorong naik ke atas Sundaland. Namun demikian, kedua pendapat tersebut menunjukkan bahwa Sumatera dibentuk oleh blok-blok benua. Ciri geokimia batuan volkanik daerah Pasaman, yang dikumpulkan dari Sumatera Barat, dengan