Showing papers in "Terra Nova in 2007"
TL;DR: The Archean Pilbara Craton contains five geologically distinct terranes (the East Pilbara, Karratha, Sholl, Regal and Kurrana Terranes) all of which are unconformably overlain by the 3.53-3.17-Ga De Grey Superbasin this article.
Abstract: The Archean Pilbara Craton contains five geologically distinct terranes – the East Pilbara, Karratha, Sholl, Regal and Kurrana Terranes – all of which are unconformably overlain by the 3.02- to 2.93-Ga De Grey Superbasin. The 3.53–3.17 Ga East Pilbara Terrane (EP) represents the ancient nucleus of the craton that formed through three distinct mantle plume events at 3.53–3.43, 3.35–3.29 and 3.27–3.24 Ga. Each plume event resulted in eruption of thick dominantly basaltic volcanic successions on older crust to 3.72 Ga, and melting of crust to generate first tonalite-trondhjemite-granodiorite (TTG), and then progressively more evolved granitic magmas. In each case, plume magmatism was accompanied by uplift and crustal extension. The combination of conductive heating from below, thermal blanketing from above, and internal heating of buried granitoids during these events led to episodes of partial convective overturn of upper and middle crust. These mantle melting events caused severe depletion of the subcontinental lithospheric mantle, making the EP a stable, buoyant, unsubductable continent by c. 3.2 Ga. Extension accompanying the latest event led to rifting of the protocontinent margins at between 3.2 and 3.17 Ga. After 3.2 Ga, horizontal tectonic forces dominated over vertical forces, as revealed by the geology of the three terranes (Karratha, Sholl and Regal) of the West Pilbara Superterrane. The c. 3.12-Ga Whundo Group of the Sholl Terrane is a fault bounded, 10-km-thick volcanic succession with geochemical characteristics of modern oceanic arcs (including boninites and evidence for flux melting) that indicate steep Archean subduction. At 3.07 Ga, the 3.12-Ga Sholl Terrane, 3.27-Ga Karratha Terrane and c. 3.2-Ga Regal Terrane accreted together and onto the EP during the Prinsep Orogeny. This was followed by development of the De Grey Superbasin – an intracontinental sag basin and widespread plutonism (2.99–2.93 Ga) as a result of orogenic relaxation and slab break off. Craton-wide compressional deformation at 2.95–2.93 Ga culminated with 2.91-Ga accretion of the 3.18 Ga Kurrana Terrane with the EP. This compression caused amplification of the dome-and-keel structure in the EP. Final cratonization was effected by emplacement of 2.89–2.83 Ga post-tectonic granites.
435 citations
Abstract: The Mozambique Ocean closed as Gondwana formed. Its suture has been identified in Madagascar (Betsimisaraka suture), but its continuation, into India, is controversial. The Palghat-Cauvery shear system appears an ideal candidate as it: (i) lies along strike of the Betsimisaraka suture in Gondwana; (ii) forms a high-pressure granulite belt; and (iii) separates crustal domains with different geological histories. However, existing age constraints have been used to suggest that the structure is Archaean/Palaeoproterozoic. Here we date metamorphic zircons using secondary ion mass spectrometry (535.0 ± 4.9 Ma) and monazites using electron probe micro-analysis (537 ± 9, 532 ± 8, 525 ± 10 Ma). No evidence for an earlier metamorphic event was found. The identification of Palghat-Cauvery high-pressure metamorphism as Cambrian, and recognition that it bounds crustal domains of contrasting origin, points to it being the southern continuation of the Betsimisaraka suture and southern margin of Neoproterozoic India.
255 citations
TL;DR: In this article, the authors demonstrate that depositional systems within the Oligocene-Early Miocene Maykop Series on either side of the Western Greater Caucasus (WGC) display a similar provenance and divergent palaeocurrents away from the range, constraining a minimum age for the subaerial uplift of the range as early as early Early-Oligocene.
Abstract: The Greater Caucasus is Europe's largest mountain belt. Significant uncertainties remain over the evolution of the range, largely due to a lack of primary field data. This work demonstrates that depositional systems within the Oligocene–Early Miocene Maykop Series on either side of the Western Greater Caucasus (WGC) display a similar provenance and divergent palaeocurrents away from the range, constraining a minimum age for the subaerial uplift of the range as early Early Oligocene. An Eocene–Oligocene hiatus, basal Oligocene olistostromes and a marked increase in nannofossil reworking also point to initial deformation in the earliest Oligocene. The initial uplift of the WGC occurred during the final assembly of the Tethysides to its south. Uplift commenced after the Late Eocene final suturing of northern Neotethys and during the initial collision of Arabia with the southern accreted margin of Eurasia. This suggests that compressional deformation was rapidly transferred across the collision zone from the indenting Arabian plate to its northern margin.
180 citations
TL;DR: In this article, the authors presented new radiometric dating for the basal Sete Lagoas cap carbonate deposits that overlie glacial units in the Sao Francisco craton, showing pristine textures and constant 87Sr/86Sr ratios around 0.7075.
Abstract: The end of the Neoproterozoic is punctuated by glacial deposition, but the chronology of these deposits is hindered presently by the paucity of geochronological data. Here, we present new radiometric dating for the basal Sete Lagoas cap carbonate deposits that overlie glacial units in the Sao Francisco craton. Six samples from aragonite-pseudomorph crystal-rich facies, showing pristine textures and constant 87Sr/86Sr ratios around 0.7075, yielded a Pb–Pb isochron age of 740 ± 22 Ma, which is interpreted as the depositional age for these remarkably preserved rocks. This age can be used to infer a low-to-moderate palaeolatitude of 20–30° for carbonate (and glacial) deposition. In addition, as it overlaps the ages obtained for the oldest Neoproterozoic glacial successions, our result reinforces the idea of a long-standing ‘Sturtian’ interval, suggesting that this event represents either different discrete glaciations or a protracted event encompassing almost 80 Ma.
164 citations
TL;DR: In this paper, the compositional fields of glaucony, Fe-illite, and Fe-Al smectites are determined in the M+/4Si vs. Fe/Sum of octahedral cations (M+ ǫ=interlayer charge).
Abstract: Iron silicate minerals are a significant component of sedimentary systems but their modes of formation remain controversial. Our analysis of published data identifies end-member compositions and mixtures and allows us to recognize controls of formation of different mineral species. The compositional fields of glaucony, Fe-illite, Fe–Al smectites are determined in the M+/4Si vs. Fe/Sum of octahedral cations (M+ = interlayer charge). Solid solutions could exist between these phases. The Fe–Al and Fe-rich clay minerals form two distinct solid solutions. The earliest phases to be formed are Fe–Al smectites or berthierine depending on the sedimentation rate. Reductive microsystems appear in the vicinity of organic debris in unconsolidated sediments. The Fe is incorporated first in pyrite and then in silicates after oxidation. Potassium ions diffuse from the sea-water–sediment interface. If not interrupted, the diffusion process is active until reaction completion is reached, i.e. formation of Fe-illite or glauconite or a mineral assemblage (berthierine–nontronite) according to the available Al ion amounts in the microsystem. Mixed-layer minerals are formed when the diffusion process is interrupted because of sedimentation, compaction or cementation. Despite the common belief of their value as palaeoenvironment indicators, these minerals can form in a variety of environments and over a period of millions of years during sediment burial.
127 citations
TL;DR: In this paper, new field data integrated by fission track analysis unravels an innovative scenario for the post-Variscan evolution of the eastern Anti-Atlas region, which is crosscut by crustal faults bearing evidence of a polyphase deformation history.
Abstract: New field data integrated by fission-track (FT) analysis unravel an innovative scenario for the post-Variscan evolution of the eastern Anti-Atlas This area, unaffected by Meso-Cenozoic tectonics according to most workers, is crosscut by crustal faults bearing evidence of a polyphase deformation history Apatite FT ages, ranging between 284 and 88 Ma, point to fast Neogene exhumation and unravel contrasting cooling paths across major faults Results show that the study area was buried beneath 2 km of allochthonous Variscan units, now eroded The eastern Anti-Atlas acted as the southern shoulder of the Atlasic rift in the Mesozoic, and underwent a dextral transpressional structuring of Neogene age followed by sub-meridian shortening The southern front of Atlasic deformation is therefore located inside the Anti-Atlas region, and it is still active
87 citations
TL;DR: In this article, the authors presented a new depth to acoustic basement map based on a grid of seismic profiles of the Western Alboran Basin, showing that the basement is more than 10 kilometres deep.
Abstract: This paper presents a new depth to acoustic basement map based on a grid of seismic profiles. In the Western Alboran Basin the basement is more than 10 km deep. An examination of a seismic profile of this region suggests that Late Oligocene–Early Miocene 5 km thick synrift formation has been accumulated in this basin. This West Alboran basin has been formed in an extensional setting, but in a fore-arc position, south of the Balearic Islands then westwards transported behind a subduction zone.
67 citations
TL;DR: In this paper, the deformation of the Ribeira-Aracuai orogen (SE Brazil) was analyzed in an eroded analogue of these orogens, and it was shown that both anatexites and magmatic intrusions display a pervasive strain-induced magmatic fabric.
Abstract: Pervasive melting of the middle crust, as inferred in Tibet and the Altiplano, probably influences the deformation of the lithosphere. To constrain strain distribution in a pervasively molten crust, we analysed the deformation in an eroded analogue of these orogens. The Ribeira-Aracuai orogen (SE Brazil) comprises a stack of allochthons containing large volumes of anatectic and magmatic rocks. The upper allochton (∼300 km long, 50–100 km wide and >10 km thick) involves peraluminous diatexites and leucogranites resulting from partial melting of the middle crust. It overlies another allochthon containing huge early- to syn-collisional plutons intruding metasediments. Both anatexites and magmatic intrusions display a pervasive strain-induced magmatic fabric. Homogeneous strain distribution suggests inefficient localization. U–Pb ages of ∼575 Ma imply that anatexite melting was synchronous to the early- to syn-collisional magmatism. Similarity in ages magmatic and solid-state fabrics indicates that intrusions and anatexites deformed coherently with solid-state rocks while still molten, in response to a combination of gravity-driven and collision-driven deformation.
66 citations
TL;DR: New fission track ages on zircon and apatite (ZFT and AFT) from the southwestern alpine paleo-accretionary wedge document a contrasting cooling history from east to west.
Abstract: New fission-track ages on zircon and apatite (ZFT and AFT) from the southwestern alpine paleo-accretionary wedge document a contrasting cooling history from east to west. In the eclogitic Monviso ophiolites, the ZFT ages are 19.6 +/- 0.8 Ma and the AFT ages are 8.6 +/- 1.7 Ma. In the HT-blueschist eastern Queyras, ZFT ages range from 27.0 +/- 1.5 Ma to 21.7 +/- 1.6 Ma and AFT ages from 14.2 +/- 2.0 to 9.4 +/- 1.1 Ma. In the LT-blueschist western Queyras, ZFT ages are between 94.7 +/- 3.1 Ma and 63.1 +/- 2.9 Ma and AFT ages are between 22.2 +/- 1.6 and 22.6 +/- 1.5 Ma. The Chenaillet ophiolite yields ages of 118.1 +/- 3.7 Ma on ZFT and of 67.9 +/- 8.5 Ma on AFT. These new FT data combined with petrological and geochronological constraints record a diachronous exhumation in the paleo-accretionary wedge during subduction and collision.
64 citations
TL;DR: In this article, the authors quantify the seismic part of the deformation in the Western and Central Alps and provide new quantitative elements about the ongoing geodynamic processes in the alpine belt.
Abstract: Neotectonics of the Western and Central Alps is characterized by ongoing widespread extension in the highest zones of the chain and transcurrent/compressive tectonics at the external limits of the belt. The overall geodetically measured deformations also indicate extension across the Western Alps. There is a good qualitative coherency between seismotectonic and geodetic approaches. Here we attempt to quantify the seismic part of the deformation. The seismic strain is compared to the deformation derived from geodesy. In sub-areas of homogeneous seismic stress/strain, we computed the total seismic moment tensor and related strain tensor. This study provides new quantitative elements about the ongoing geodynamic processes in the alpine belt. The important discrepancies obtained between seismic strains and geodetically-measured deformations raise the issue of aseismic deformation in the Alps, which could be related to elastic loading, creeping and/or a slower ductile-style deformation.
63 citations
TL;DR: A-type magmatism in the Gawler Craton, Curnamona Province and eastern Mount Isa Inlier is interpreted as a segment of a hotspot track that evolved between c. 1600 and 1500 Ma.
Abstract: Mesoproterozoic A-type magmatic rocks in the Gawler Craton, Curnamona Province and eastern Mount Isa Inlier, form a palaeo-curvilinear belt for reconstructed plate orientations. The oldest igneous rocks in the Gawler Craton are the Hiltaba Granite Suite: c. 1600–1575 Ma. The youngest in the Mount Isa Inlier are the Williams-Naraku Batholiths: c. 1545–1500 Ma. The belt is interpreted as a segment of a hotspot track that evolved between c. 1600 and 1500 Ma. This hotspot track may define a quasilinear part of Australia’s motion between 1636 and 1500 Ma, and suggests that Australia drifted to high latitudes. An implication of this interpretation is that Australia and Laurentia may not have been fellow travellers leading to the formation of Rodinia. A hotspot model for A-type magmatism in Australia differs from geodynamic models for this style of magmatism on other continents. This suggests that multiple geologic processes may be responsible for the genesis of Proterozoic A-type magmas.
TL;DR: In this paper, organic matter from the cap dolostones overlying the Marinoan-age glacigenic diamictites of the Araras Group, Amazon craton, has been studied to reconstruct the post-glacial ecosystem.
Abstract: Organic matter from the cap dolostones overlying the Marinoan-age glacigenic diamictites of the Araras Group, Amazon craton, has been studied to reconstruct the post-glacial ecosystem. Molecular fossils indicate that the post-Marinoan ecosystem was marked by an apparent decline in marine algal diversity. The proliferation of red algae may be explained by environmental changes, such as a massive nutrient input accompanying continental weathering after the ice thaw and a dimer light penetrating sea water due to the drowning of the platform. In addition, the presence of green sulphur bacteria indicates that sea water was stratified with an anoxic (possibly euxinic, i.e. sulphidic) layer at the water–sediment interface. Sulphur cycling probably occurred at the redox boundary as suggested by the recognition of active sulphate reduction. This observation supports a microbially induced model for the formation of the cap dolostones.
TL;DR: In this article, a detachment fault separating high-pressure/low-temperature (HP-LT) metamorphic lower from non-metamorphic upper tectonic units on Crete is described.
Abstract: Crustal extension in the overriding plate at the Aegean subduction zone, related to the rollback of the subducting African slab in the Miocene, resulted in a detachment fault separating high-pressure/low-temperature (HP-LT) metamorphic lower from non-metamorphic upper tectonic units on Crete. In western Crete, detachment faulting at deeper crustal levels was accompanied by structural disintegration of the hangingwall leading to the formation of half-graben-type sedimentary basins filled by alluvial fan and fan-delta deposits. The coarse-grained clastic sediments in these half-grabens are exclusively derived from the non-metamorphic units atop the detachment fault. Being in direct tectonic contact with HP-LT metamorphic rocks of the lower tectonic units today, the basins must have formed in the period between c. 20 and 15 Ma, prior to the exposure of the HP-LT metamorphic rocks at the surface, and juxtaposed with the latter during ongoing deformation.
TL;DR: In this paper, a structural and kinematic study of the Hospitalet dome (Pyrenees) is presented, which corresponds to the eastern half of an EW-trending antiformal structure made of an orthogneissic core intruded by granitoids, partly covered by Upper Proterozoic to Lower Ordovician metapelites.
Abstract: A new structural and kinematic study of the Hospitalet dome (Pyrenees) is presented. This dome corresponds to the eastern half of an EW-trending antiformal structure made of an orthogneissic core intruded by granitoids, partly covered by Upper Proterozoic to Lower Ordovician metapelites. Its Variscan evolution can be split into four stages: (i) development of a strong high temperature pervasive deformation associated with subhorizontal foliations and lineations, and with non-coaxial top-to-the-east kinematics; (ii) formation of a south-verging overturned megafold; (iii) emplacement of calc-alkaline granitoids; and (iv) formation of mylonitic bands on the southern border of the dome, with reverse dextral kinematics. The flat lying pervasive high-T deformation is interpreted as a large lateral flow developed in a dextral transpressive regime inducing an important uncoupling between the middle and upper crusts. The next stages happened in a progressive deformation in the same transpressive regime.
TL;DR: In this paper, the authors investigated Lake Cheko, located ∼8 km NNW of the inferred Tunguska explosion epicenter, and revealed that the lake fills an impact crater.
Abstract: The so-called ‘Tunguska Event’ refers to a major explosion that occurred on 30 June 1908 in the Tunguska region of Siberia, causing the destruction of over 2000 km2 of taiga, globally detected pressure and seismic waves, and bright luminescence in the night skies of Europe and Central Asia, combined with other unusual phenomena. The ‘Tunguska Event’ may be related to the impact with the Earth of a cosmic body that exploded about 5–10 km above ground, releasing in the atmosphere 10–15 Mton of energy. Fragments of the impacting body have never been found, and its nature (comet or asteroid) is still a matter of debate. We report results from the investigation of Lake Cheko, located ∼8 km NNW of the inferred explosion epicenter. Its funnel-like bottom morphology and the structure of its sedimentary deposits, revealed by acoustic imagery and direct sampling, all suggest that the lake fills an impact crater. Lake Cheko may have formed due to a secondary impact onto alluvial swampy ground; the size and shape of the crater may have been affected by the nature of the ground and by impact-related melting and degassing of a permafrost layer.
TL;DR: In this paper, the authors present new field observations from a region south of Lago General CarreraBuenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5−4 Ma and after 3 Ma.
Abstract: Recent field work and review of radiometric data obtained from Neogene lavas and plutonic rocks exposed in the Eastern Central Patagonian Cordillera (46‐48oS), which overlie subducted segments of the South Chile Ridge, suggest important Late Miocene to Pleistocene morphological changes in relation to base level variations and ⁄or tectonic events. We present new field observations from a region south of Lago General CarreraBuenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5‐4 Ma and after 3 Ma. We also show that the 12 Ma basaltic flows of the Meseta del Lago Buenos Aires (2000 m a.s.l.) have been subjected to deep incision, with younger lavas dated at 1.2 Ma partially filling the valleys. These incisions are thought to reflect progressive eastward tilting of the entire meseta. Our new observations, together with additional features from Central Patagonia, strongly suggest that tectonic events led to a regional widespread morphological change after 5 Ma. The coincidence in time and space between the subduction of segments of the South Chile Ridge at 6 and 3 Ma causing opening of a slab window, and strong base level variations in the studied area, suggests a cause-and-effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. The uplift is purely tectonic in origin and occurred prior to the subduction of the South Chile Ridge. Extension should be a consequence of this subduction.
TL;DR: In this paper, a new model is proposed, which comprises a south-east-dipping South Loyalty basin slab that retreated south-westward in the Eocene-early Miocene and was continuous with the north-eastdipping subduction zone of New Caledonia.
Abstract: Oligocene–Miocene models for northern New Zealand, involving south-westward subduction to explain Early Miocene Northland volcanism, do not fit within the regional Southwest Pacific tectonic framework. A new model is proposed, which comprises a north-east-dipping South Loyalty basin slab that retreated south-westward in the Eocene–earliest Miocene and was continuous with the north-east-dipping subduction zone of New Caledonia. In the latest Oligocene, the trench reached the Northland passive margin, which was pulled it into the mantle by the slab, resulting in obduction of the Northland allochthon. During and after obduction, the slab detached from the unsubductable continental lithosphere, inducing widespread calc-alkaline volcanism in Northland. The new model further explains contemporaneous arc volcanism along the Northland Plateau Seamount Chain and sinking of the Northland basement, followed by uplift and extension in Northland.
TL;DR: In this article, the authors report data on particle shape from natural cataclastic rocks in poorly layered carbonates in the Apulian foreland of the Southern Apennines of Italy.
Abstract: A fundamental yet still unresolved puzzle provided by cataclasis is whether particle size reduction mostly progresses through time by the same fragmentation mechanism or not. Available field, laboratory and numerical modelling results on the evolution of cataclastic rocks are still controversial. The evidence that cataclastic rocks exert a primary control on the frictional strength, stability, seismic velocity and permeability properties of fault zones encourages further research on cataclasis. Here, we report data on particle shape from natural cataclastic rocks in poorly layered carbonates in the Apulian foreland of the Southern Apennines of Italy. Particle shape analyses show that particle angularity decreases with increasing size and, for a given size class, it decreases with increasing fractal dimension of the particle size distribution. These results offer support to the temporally and spatially variable nature of rock comminution.
TL;DR: In this paper, the authors present experiments of upraising and relaxing topographies showing that peneplanation can occur above the ultimate base level (sea level), after active uplift, the erosion of a topography bounded by a piedmont generates a final smooth and highly elevated topography.
Abstract: We present experiments of upraising and relaxing topographies showing that peneplanation can occur above the ultimate base level (sea level). After active uplift, the erosion of a topography bounded by a piedmont generates a final smooth and highly elevated topography. Smoothing at high elevation is even possible during active uplift if the evolution of topography is disrupted by the deposition of the products of erosion on its piedmont which is the case at the transition from underfilled to overfilled conditions in foreland basins.
TL;DR: In this article, the authors quantified the long-term rates of migration and shortening of the Apennine fold-and-thrust system along with the measurement errors.
Abstract: : Is compression across the northern Apennine fold-and-thrust system (Italy) still active? To address this question we quantified the long-term rates of migration and shortening of the system along with the measurement errors. Our approach integrates structural geology, seismicity patterns, and statistical treatment of tectonic activity. Based on recently published surface and subsurface data, we found a migration rate of 8.85+/-0.61 mm/y . The inception age of individual fold structures follow closely this average rate, indicating that the system has been migrating at a constant rate for the past 17 Myr. Cumulative shortening of the system also increases linearly through time at 2.93+/-0.31 mm/y . The location of the youngest structures in the easternmost portion of the system coincides with a significant peak of seismic moment released by historical earthquakes. We conclude that not only these easternmost thrusts are still active, but also that they generate earthquakes. Keywords
TL;DR: In this article, the dates of zircon cores and rims from granulites from the uppermost NW Iberian Massif were used to study the complex relationship between magmatism and metamorphism in the deep roots of arc environments.
Abstract: Dating of zircon cores and rims from granulites developed in a
shear zone provides insights into the complex relationship
between magmatism and metamorphism in the deep roots of
arc environments. The granulites belong to the uppermost
allochthonous terrane of the NW Iberian Massif, which forms
part of a Cambro-Ordovician magmatic arc developed in the
peri-Gondwanan realm. The obtained zircon ages confirm that
voluminous calc-alkaline magmatism peaked around 500 Ma
and was shortly followed by granulite facies metamorphism
accompanied by deformation at c. 480 Ma, giving a time
framework for crustal heating, regional metamorphism, deformation
and partial melting, the main processes that control the
tectonothermal evolution of arc systems. Traces of this arc can
be discontinuously followed in different massifs throughout the
European Variscan Belt, and we propose that the uppermost
allochthonous units of the NW Iberian Massif, together with the
related terranes in Europe, constitute an independent and
coherent terrane that drifted away from northern Gondwana
prior to the Variscan collisional orogenesis.
TL;DR: In this article, the authors used dislocation models and available structural and geochemical information indicate that the subsidence is due to crack closure processes along two main ENE•WSW and E•W preexisting faults, which represent the preferred pathway of CO2 degassing from the hydrothermal system located beneath Mt Epomeo.
Abstract: Levelling surveys carried out between 1990 and 2003 on the Mt Epomeo resurgent block (Ischia Island) record negative dislocations on its northern and southern flanks with a maximum subsidence rate of 1.27 cm yr )1 . This deformation is not associated with the cooling, crystallization or lateral drainage of magma and cannot be explained by a pressure point or prolate ellipsoid source. Results from dislocation models and the available structural and geochemical information indicate that the subsidence is due to crack closure processes along two main ENE‐WSW and E‐W preexisting faults, which represent the preferred pathway of CO2 degassing from the hydrothermal system located beneath Mt Epomeo. The monitoring of the dislocations and CO2 flux along these faults could give useful information on the dynamics of the hydrothermal system.
TL;DR: The Isola del Toro volcanic rocks represent the first anorogenic products produced during the opening of the western Mediterranean Sea as discussed by the authors, and they have an age of 11.83 ± 0.10 Ma.
Abstract: The Isola del Toro is a small island (� 1k m 2 ) about 5 nautical miles SW of Sardinia entirely made up of mildly alkaline sodic evolved rocks (benmoreites and trachytes) related to each other by fractionation processes. 40 Ar/ 39 Ar dating of an anorthoclase mineral separate from a trachyte gave an age of 11.83 ± 0.10 Ma. This age estimate falls within an interval previously considered a-magmatic in Sardinia. The results of this study shift the beginning of the Middle Miocene–Quaternary anorogenic volcanism of Sardinia back to the Late Serravalian. The transition between orogenic and anorogenic activity in Sardinia is markedly different from that recorded in the rest of the circum-Mediterranean area, where this transition is much more gradual, both in time and in terms of magma composition. On the other hand, the transition between orogenic and anorogenic magmatism in Sardinia is rather sharp and lacks hybrid compositions. The Isola del Toro volcanic rocks represent the first anorogenic products produced during the opening of the western Mediterranean Sea.
TL;DR: A hydrogeophysical study was carried out by a water controlled injection within a landslide situated on an active part of the La Clapiere landslide foot (Alpes Maritimes, France).
Abstract: A hydrogeophysical study was carried out by a water controlled injection within a landslide situated on an active part of the La Clapiere landslide foot (Alpes Maritimes, France). Coupling of both real-time geophysical and hydrological follow ups allowed the representation and quantification of the surface water drainage in space and time within the slipped mass. Thus, 30% of the injected water is quickly drained by a complex slipping surface meanly situated at 10-m depth. The transit time between injection and outflow of the water allowed an overloading of about 10 m3 (i.e. 10 tons) comparable with classical rain events in the area. This weight and the associated interstitial pressures increase have not led to any movements asking for the origin of the water volumes which could induce destabilizations. This experiment enabled an accurate redefinition of the internal slope structure and the understanding of the dynamics of the slipped mass with a surface hydraulic request.
TL;DR: In this article, trace fossils described in Chengjiang have been well preserved in connection with certain pliable carapaces or skeletons of the Chengjiang animals, suggesting that some bilaterians of uncertain affinities seem to have been active at the burial site.
Abstract: Diminutive trace fossils described here have been well preserved in connection with certain pliable carapaces or skeletons of the Chengjiang animals. Taphonomic evidence suggests that these traces were formed in situ. The peculiar preservation indicates that some bilaterians of uncertain affinities seem to have been active at the burial site, constituting an important group of the hidden majority of Cambrian marine community. This may be an essential feature closely associated with the palaeoecology and exceptional preservation of the Cambrian fossil Lagerstatten. The rare preservation of such millimetre-sized trace fossils raises further doubts about the timing of the initial benthic bilaterians by applying trace fossil evidence.
TL;DR: In this paper, it was shown that the lower (hot) side of a subducting slab entrains by the formation of a ∼10-30 km-thick downdragged layer, whose thickness depends upon the subduction rate and the density contrast and viscosity of the asthenosphere.
Abstract: Laboratory and numerical experiments and boundary layer analysis of the entrainment of buoyant asthenosphere by subducting oceanic lithosphere implies that slab entrainment is likely to be relatively inefficient at removing a buoyant and lower viscosity asthenosphere layer. Asthenosphere would instead be mostly removed by accretion into and eventual subduction of the overlying oceanic lithosphere. The lower (hot) side of a subducting slab entrains by the formation of a ∼10–30 km-thick downdragged layer, whose thickness depends upon the subduction rate and the density contrast and viscosity of the asthenosphere, while the upper (cold) side of the slab may entrain as much by thermal 'freezing' onto the slab as by mechanical downdragging. This analysis also implies that proper treatment of slab entrainment in future numerical mantle flow experiments will require the resolution of ∼10–30 km-thick entrainment boundary layers.
TL;DR: In this paper, three metapelitic xenolith suites in the Neogene Volcanic Province (NVP) of SE Spain (from SW to NE: El Hoyazo, Mazarron and Mar Menor) originated by partial melting at different crustal depths, decreasing from 20-25km in the SW to 9-12 km in the NE.
Abstract: Three metapelitic xenolith suites in the Neogene Volcanic Province (NVP) of SE Spain (from SW to NE: El Hoyazo, Mazarron and Mar Menor) originated by partial melting at different crustal depths, decreasing from 20–25 km in the SW to 9–12 km in the NE. Peak temperatures reached c. 900 °C. The xenolith source level is equated with the base of a felsic upper crust of high melting potential (‘fertility’). At El Hoyazo, this matches a thin, intracrustal low-velocity zone recently inferred from seismic studies. Isostatic calculations indicate that this zone increases in thickness from SW to NE. A model of increasing upper crustal thinning from SW to NE in the NVP, accompanied by mafic underplating, is consistent with the 9 Ma petrological data, with current heat flow, seismic data and gravimetry. It is concluded that significant crustal extension occurred in the NVP in the late Miocene, i.e. after the main phase of widespread extension, exhumation of high-pressure rocks and formation of the Alboran Sea.
TL;DR: In this article, an accurate analysis of strain parameters, computed by inversion of SW electro-optical distance data, suggested that the observed strong displacements on this flank of the edifice can also be related to dextral shear movements along a roughly NE−SW buried fault crossing the area covered.
Abstract: Surface deformations on the western flank of Mt Etna volcano, spanning 1980‐2004, have been analysed as they pertain to stress interactions between magma intrusions within the shallow crust along the S‐SE Rift and faulting sensitivity. During this period, an accurate analysis of strain parameters, computed by inversion of SW electro-optical distance data, suggested that the observed strong displacements on this flank of the edifice can also be related to dextral shear movements along a roughly NE‐SW buried fault crossing the area covered
TL;DR: In this paper, a post-collisional extensional framework is proposed to explain the late Hercynian tectonic evolution of the Calabria crust, which is characterized by peak metamorphic conditions up to 800 ÂC and 1000 ÂMPa.
Abstract: The late Hercynian tectonic evolution of the Calabria crust is characterized by peak metamorphic conditions up to 800 °C and 1000 MPa, and coeval mid-crustal granitoid emplacement at 304–300 Ma. To check if a post-collisional extensional framework, similar to that of other Hercynian massifs, can explain petrologic data, we model the pressure–temperature evolution of the crust during extension following granitoid emplacement. Model parameters are constrained by petrologic, geochemical and structural data. Computed P–T paths are characterized by nearly isothermal decompression followed by isobaric cooling, which show a good fit to petrologic P–T paths for duration of extension between 5 and 10 Ma. The model results, therefore, support an interpretation of the magmatic and metamorphic evolution of the Calabria crust in terms of the late Hercynian extension. In this framework, slab break-off is a reasonable explanation for the common evolution of the southern European Hercynian massifs.
TL;DR: In this paper, a mollusc-based meta dataset of 859 d 13 C and d 18 O data of Miocene nearshore settings in the European Paratethys Sea and its descendant Lake Pannon was used to understand isotope trends in epicontinental seas.
Abstract: Analyses were made of a mollusc-based meta dataset of 859 d 13 C and d 18 O data of Miocene nearshore settings in the European Paratethys Sea and its descendant Lake Pannon. The observed trends document a strong tie to geodynamics, which are largely decoupled from Miocene open ocean isotope curves. Semi- to fully enclosed, initially marine water bodies such as the Paratethys Sea are prone to switching seawater isotope signatures because they respond rapidly to changes in the evaporation ⁄precipitation ratio. Two phases of positive deviations of oxygen isotope values of water (relative to the modern ocean value, SMOW) occurred during the Middle Miocene; both were initiated by tectonic constrictions of the seaways and became amplified by global warming and regionally decreasing precipitation. With the final disintegration of the Paratethys, the marine isotope signatures vanish. Instead, the observed isotope trends suggest a comparably simple system of an alkaline lake with steadily declining salinity. The oceanderived Paratethys Sea may thus act as a key for understanding isotope trends in epicontinental seas.