Himalayas where erosion, resulting of the interplay between climate and tectonics shapes the most... more Himalayas where erosion, resulting of the interplay between climate and tectonics shapes the most spectacular landscapes on the planet. But what about more internal and deepest surface fluid infiltration? Here we report analysis of the δ 18 O (water) and δD (water) of extracted water from fluid inclusions hosted into Cenozoic quartz veins sampled in the core of the Himalayan range, near the Main Central Thrust and the South Tibetan Detachment. Isotopic and microthermometric values suggest a meteoric origin for the fluids trapped in the quartz of syn-to post-kinematic veins formed between 10 to 20 km depth. Moreover, the isotopic compositions obtained in this study on quartz fluid inclusions water collected along a transect across the Himalayan range evolved with the topography in a similar manner than the modern meteoric water. Considering the age of formation of the quartz veins between 18 and 12 Ma, we deduce that the morphology of the Himalayan topographic front was already shaped during the Miocene but located further north.
Journal of South American Earth Sciences, Aug 1, 2017
In subduction settings, the tectonic regime of the overriding plate is closely related to the geo... more In subduction settings, the tectonic regime of the overriding plate is closely related to the geometry of the subducting plate. Flat-slab segments are supposed to increase coupling at the plate interface in the Andes, resulting in an increase and eastward migration of the shortening in the overriding plate. Above the Peruvian flat-slab, a 200 km-long normal fault trend parallel to the range and delimits the western flank of the Cordillera Blanca. In a context of flat subduction, expected to produce shortening, the presence of the Cordillera Blanca normal fault (CBNF) is surprising. We performed a systematic inversion of striated fault planes in the Cordillera Blanca region to better characterize the stress field above the Peruvian flat-slab. It evidences the succession of different tectonic regimes. NE-SW extension is predominant in most of the sites indicating a regional extension. We suggest that the Peruvian flat-slab trigger extension in the Western Cordillera while the shortening migrated eastward. Finally, we propose that flat-slab segments do not increase the coupling at the trench neither the shortening in the overriding plate but only favor shortening migration backward. However, the stress field of the overriding plate arises from the evolution of plate interface properties through time due to bathymetric anomaly migration.
The Sardinia Channel is located in a 400 km-long submerged section of the Apennine-Maghrebian bra... more The Sardinia Channel is located in a 400 km-long submerged section of the Apennine-Maghrebian branch of the Alpine chain. The Sardinia Channel connects the Algerian-Ligurian-Provençal to the Tyrrhenian oceanic basins. The structure of this region results from the superposition of two tectonic regimes: an earlier crustal thickening and a later crustal thinning. The crustal thickening is the consequence of the shortening which occurred in the late Oligocene-early Miocene during the build up of the Apennine-Maghrebian Orogen. This thickening is coeval with the rotation of the Corsican-Sardinian block and the opening of the Provençal-Algerian back-arc basin. All of these structures, as well as the magmatic arcs in Sardinia and Tunisia, i.e. the Galite Archipelago, are connected to the subduction of the Tethyan Ocean. The crustal thinning is associated with the rifting of the Tyrrhenian Basin, which occurred just before the Messinian salinity crisis and was accompanied by significant erosion throughout the region. This erosion was followed by a period of thermal subsidence linked to the opening of the Tyrrhenian oceanic basin in the Plio-Quaternary, interspersed with minor episodes of compression. On the Sardinian margin, the dives led to the discovery of a submarine volcano, dated at 12.6 Ma, and composed of shoshonitic andesites with lamprophyre inclusions, and to the characterization of the nature and structure of the underlying basement, consisting of tilted blocks of Hercynian metamorphic and granitic rocks and their sedimentary cover. The sea floor morphology reflects this structure. The other areas of the Sardinia Channel explored, i.e. its southern margin and central ridge, belong to the Calabrian-Peloritanian-Kabylian group (CPK). They are composed of a metamorphic and granitic Hercynian basement deformed during the Alpine orogeny, which is stratigraphically overlain by an Oligo-Miocene detrital cover of Peloritanian or Kabylian type, and tectonically overlain by the so-called "flysch nappe". Throughout the CPK domain these formations were subjected during the Oligo-Miocene, at ca. 23 Ma ago, to a first denudation event, and during the Tortonian, ca. 10-8 Ma ago, to a second denudation, which has been connected to the opening of the Tyrrhenian basin. Structures, microstructures and thermochronological data indicate relatively low P-T conditions for the extensional deformations: this suggests that these units remained at shallow depths in the Apennine-Maghrebian Orogen, and were relatively preserved from the Messinian erosion. The age (12.5 Ma) and nature of the volcanic sequence in the Sorelles is closely comparable with the calc-alkaline suite of the Galite Archipelago, Tunisia. Thus, the data gathered during the dives in the Sardinia Channel give new constraints to the reconstruction of the kinematic evolution not only of the region, but also to the entire western Mediterranean. Structure du canal de Sardaigne : réamincissement crustal et extension tardi-orogénique au sein de la chaîne Apennino-Maghrébienne ; résultats des campagnes de plongées Cyana SARCYA et SARTUCYA en Méditerranée occidentale Mots clés.-Méditerranée occidentale, Canal de Sardaigne, Exploration en submersible, Evolution géodynamique néogène, Réamincissement crustal. Résumé.-Le canal de Sardaigne est installé sur un segment immergé de la branche Apennino-Maghrébide de la Chaîne alpine long de 400 km ; il assure une communication profonde entre les bassins océaniques Algéro-Liguro-Provençal et Tyrrhénien. Les structures de ce domaine résultent de la superposition de deux régimes tectoniques successifs, d'abord d'épaississement crustal, suivi d'un réamincissement. Ce dernier est associé au rifting Tyrrhénien ; il s'est produit juste avant la crise messinienne ; celle-ci a entraîné une importante érosion de tout le domaine. Une période de subsidence thermique liée à l'ouverture océanique du bassin Tyrrhénien caractérise ensuite le Plio-Quaternaire, pendant lequel se produisent cependant des épisodes mineurs d'inversion.
The postseismic deformation consecutive to the April 25, 2015 Gorkha earthquake (Mw 7.9) is estim... more The postseismic deformation consecutive to the April 25, 2015 Gorkha earthquake (Mw 7.9) is estimated in this paper based on a cGNSS network installed prior to the earthquake and supplemented by 6 cGNSS stations installed after the main shock. Postseismic displacement are obtained from daily time series corrected for interseismic deformation and seasonal variations. The maximum postseismic displacement is found north of the rupture area, where locally it reached 100 mm between the date of the earthquake and late 2016. The postseismic deformation affects the northern part of the rupture area but not the southern part, along the
More than 15 years of field and laboratory investigations on samples from Terre Adélie to the wes... more More than 15 years of field and laboratory investigations on samples from Terre Adélie to the western part of George V th Land (135 to 146°E) during the GEOLETA program allow a reassessment of the Terre Adélie Craton (TAC) geology. The TAC represents the largest exposed fragment of the East Antarctic Shield preserved from both Grenville and Ross tectono-metamorphic events. Therefore it corresponds to a well-preserved continental segment that developed from the Neoarchean to the Paleoproterozoic. Together with the Gawler Craton in South Australia, the TAC is considered as part of the Mawson continent, i.e. a striking piece of the Rodinia Supercontinent. However, this craton represents one of the less studied parts of the East Antarctic Shield. The three maps presented here clearly point out the extent of two distinct domains within the Terre Adélie Craton and suggest that the TAC was built up through a polyphased evolution during the Neoarchean-Siderian (c.a. 2.5Ga) and the Statherian (c.a. 1.7Ga) periods. These data support a complete re-assessment of the TAC geology and represent a valuable base for the understanding of global geodynamics changes during Paleoproterozoic times.
Tectonometamorphic evolution of the central Karakorum (Baltistan, northern Pakistan)
Tectonophysics, 1996
New structural and metamorphic data from the Chogo Lungma glacier area and Basha valley enlighten... more New structural and metamorphic data from the Chogo Lungma glacier area and Basha valley enlighten the polyphased tectonometamorphic evolution of the Metamorphic Complex of Karakorum. A pre- to early D1 event is defined by a metamorphic cleavage in the core of some zoned garnet and staurolite porphyroblasts. The main tectonometamorphic event (D1) is characterized by N110°E south-vergent isoclinal folds associated
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1999
Granite and gneiss have been sampled on the submarine fault scarps of the Sardinia Channel and ha... more Granite and gneiss have been sampled on the submarine fault scarps of the Sardinia Channel and have been dated using the ""ArY3"Ar method. The majority of rocks partially preserve Hercynian ages. Some of them display Lower Cretaceous .lge.s. In addition, Upper Eocene-Oligocene argon resetting is recorded only in rocks from the southeast sector of the Channel. We thus propose that the basement of the Sardinid Channel occupied a shallow position within the stack of the Alpine tectonic units, behind the more deformed front of the internal zones of the Maghrebide Chain. (0 Academic des sciences / Elsevier, Paris.) * Correspondance et tires B part.
The Shyok Suture Zone of the Ladakh palaeovolcanic arc is made of Cretaceous volcanosedimentary f... more The Shyok Suture Zone of the Ladakh palaeovolcanic arc is made of Cretaceous volcanosedimentary formations intruded by granodioritic plutons. Field observations show a tectonic stacking of litho-units from different volcanic arc and back-arc environments. In the western part (Skardu area), the Shyok Suture Zone can be subdivided into two groups: (1) The Northern Group, which consists of olistolith basaltic blocks and tuffs. The basalts are LREE depleted with a LILE enrichment and a slight Nb depletion suggesting a back-arc basin origin. (2) The Southern Group, which consists predominantly of andesites that show LREE enrichment, a flat HREE pattern, strong Nb-Ta depletion, and LILE enrichment. The volcanic rocks of the Southern Group appear to have island-arc tholeiite (IAT) to calc-alkaline affinities. In the eastern part of the suture zone (Nubra-Shyok area), Albian to Cenomanian age silicoclastic sediments predominate. These sediments correspond to a large detrital platform built on the northern part of the Ladakh Arc. At the top, these sediments interlayer with basaltic to andesitic lavas. These lavas appear to be more differentiated and calc-alkaline in nature than the Skardu Southern Group lavas, but show similar volcanic arc affinities. No evidence of a back-arc basin was found in this area. Our data from these two areas shows a northwest-southeast evolution, from back-arc to arc formations in northern Ladakh. Opening of this back-arc basin occurred on the northwestern side of the Ladakh Arc. This back-arc was progressively closing eastward. The arc itself was more mature in the east, resembling the southern Tibetan continental arc, and was characterised by more continental sedimentation. Subsequent Himalayan tectonometamorphic evolution, closure of the back-arc basin and deformation along the Shyok Suture, reflects an early asymmetrical geometry along the Asian margin and Kohistan-Ladakh Arc.
In central Nepal, the Tibetan Slab is made up of biotite-gneisses (metapelites and metagreywackes... more In central Nepal, the Tibetan Slab is made up of biotite-gneisses (metapelites and metagreywackes), orthogneisses (metagranites) and migmatites. Melanosomes are generally biotite-(f muscovite)-bearing, but locally they may be tourmaline-rich when associated with boron-rich granitic material. Leucosomes occur as lenses conformable with the foliation, veins, patches, or as fillings in shear zones and extensional structures. Field relationships, and mineralogical and chemical data show that three processes may have contributed to the formation of the Tibetan Slab leucosomes: metamorphic differentiation or disequilibrium partial melting (low-Zr tonalitic leucosomes), in-situ equilibrium partial melting (high-Zr leucosomes and some granitic leucosomes) and injection of externally-derived melts (most granitic and some tonalitic leucosomes). The Manaslu pluton belongs to the High Himalayan leucogranite belt and was emplaced at the top of the Tibetan Slab. It corresponds to a muscovite-biotite leucogranite that has been assumed to derive from melting of the Tibetan Slab gneisses (Formation I). Phase relationships, a more magnesian chemistry of the ferromagnesian minerals from the Tibetan-Slab migmatites as compared to the Manaslu leucogranite, the microtextures of accessory phases, and trace-element compositions (lower U, Li, F and higher Sr, Eu, Y, Yb contents in the migmatite leucosomes) show that the in situ Himalayan migmatites, at the crustal level presently exposed, have not been produced under the same P-T-X,Io conditions as the Manaslu leucogranite magma. While the Formation I was the probable source for the Manaslu granite, migmatites within the formation are not the remanants of a melting process from which the Manaslu granite was derived. Both the Tibetan Slab migmatites and the Manaslu leucogranite may be considered as evidence of dehydration and melting at deeper crustal levels, and of percolation of melts and hydrothermal fluids through the crust.
Kashmir earthquake ruptured an out-of-sequence Himalayan thrust known as the Balakot-Bagh thrust.... more Kashmir earthquake ruptured an out-of-sequence Himalayan thrust known as the Balakot-Bagh thrust. The earthquake's hypocenter was located at a depth of 15 km on the ramp close to a possible ramp/flat transition. In the weeks following the earthquake a GPS network was installed to measure postseismic displacement. The initial measurements in November 2005 were followed by other campaigns in January and
Evolution à pression et température élevées d'inclusions fluides dans un quartz synthétique
Bulletin de Minéralogie, 1984
Des echantillons d'un monocristal de quartz synthetique contenant des inclusions fluides (I.F... more Des echantillons d'un monocristal de quartz synthetique contenant des inclusions fluides (I.F.) ont ete chauffes dans un autoclave (T = 448 °C, correspondant a une pression interne Pi de 282 MPa dans les inclusions). La pression d'argon de confinement etait soit inferieure (Pc = 200 MPa, duree 69 a 3 064 h) soit superieure (Pc = 350 MPa, duree 2 086 h) a Pi. La comparaison des I.F. avant et apres experience montre qu'elles ont subi des changements importants de forme et des variations mesurables de la densite. Deux processus d'evolution sont observes et discutes : — Reequilibrage rapide par decrepitation et apparition d'I.F. secondaires. La forte diminution de la densite des inclusions s'explique par l'augmentation de volume de la cavite lors de la decrepitation. Un nouvel equilibre tel que Pi ⋍ Pc est indique par les mesures de Th. — Les I.F. non decrepitees montrent une evolution progressive de leurs forme et densite. Des formes en cristaux negatifs sont rapidement atteintes et leur rapport L/l decroit jusqu'a une valeur limite de 3 environ. Quand Pi est superieure a Pc, Th augmente progressivement avec le temps (Δ Th atteignant 10 °C, c'est-a-dire une diminution de la densite de 0,015). Une diffusion d'OH- et une rehydratation du quartz hote sont proposees comme explication possible de la diminution de la densite. Quand Pi est inferieure a Pc, la densite des I.F. augmente et ce phenomene reste encore inexplique.
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1997
Two new occurrences of HP rocks have been found in the Indus suture zone on the eastern side of t... more Two new occurrences of HP rocks have been found in the Indus suture zone on the eastern side of the Nanga Parbat-Haramosh massif: a retrogressed eclogitic assemblage in pyroxenitic boudins within the Iadakh island-arc sequence, and an HP granulitic paragenesis in mafic alternations of High Himalaya banded gneisses. PT estimates on five samples with garnet-clinopyroxene-amphiboleplagioclase-quartz-FeTi oxide-biotite mineral assemblage have respectively yielded 13 + 1 kbar for 610 rt 30 OC, and 10 f 1 kbar for 700 & 50 'C. This metamorphism is linked to the continuous subduction of continental and arc material after India-Eurasia collision. The granulitic retrogression corresponds to a phase of collage, with prograde granulites during exhumation.
This paper presents TrackDip, a new method for dipmeter data processing. This method selects, loc... more This paper presents TrackDip, a new method for dipmeter data processing. This method selects, localizes and measures significant tilts from the comparison at various scales of the changes of orientation of sedimentary beddings. We tested this method on simple cases (unconformity, gradual tilt, successive tilts, without and with additional random noise) and on a field example, along three sections in the Eocene Sobrarbe delta, Ainsa foreland basin, northern Spain. For synthetic data sets, the method clearly identifies and measures the introduced tilts. On the field, sedimentary and tectonic structures, especially three main syn-sedimentary sliding surfaces (S1 to S3), were successfully identified from processed dipmeter data. The tilt axis are mainly trending N-S in sandstones, associated to westward transport of sediments. The sliding surfaces S1 and S3 correspond to E-W-trending tilt axis, tentatively correlated either to the flexural subsidence of the basin, or to anticline growth during sedimentation south of the studied area. Combination of these sedimentary and tectonic directions results in a NE-SW striking submarine slope, which locally controls the gravitydriven deformations, especially on the S2 sliding surface. Finally, NNW-SSE-trending tilts above the uppermost S3 sliding surface are interpreted as the result of infilling on the side of the scar produced by sliding.
Metamorphic and Magmatic Evidences fo Neogenous Slab Breakoff Beneath S-Karakorum and S-Tibet
On the S- Karakorum margin, Neogene granulites define an east-west trending thermal anomaly. Thes... more On the S- Karakorum margin, Neogene granulites define an east-west trending thermal anomaly. These rocks have been heated from 600 to 750° C during a slight pressure drop, from 0.7 to 0.5 GPa. Their retrogressive path cross-cuts the relaxed geotherm of tectonically thickened crust. Such a P-T evolution can be obtained only if an advective source of heat is involved.
Slow steady exhumation of the high elevation Deosai Plateau (Northern Pakistan Himalaya) since 40 Ma
Mountain ranges of the north-western Himalaya in Pakistan show strongly contrasting relief, oppos... more Mountain ranges of the north-western Himalaya in Pakistan show strongly contrasting relief, opposing steep, deeply incised topography with extremely high peaks such as the Karakorum Range and Nanga Parbat Haramosh Massif (NPHM), to high-altitude, low-relief areas such as the Deosai Plateau located between the Karakorum and NPHM and the Tso-Morari Massif in Eastern Ladakh. In contrast, mean elevations of the
Experimental decrepitation and re-equilibration of fluid inclusions in synthetic quartz
Tectonophysics, 1981
... in The Netherlands EXPERIMENTAL DECREPITATION AND RE-EQUILIBRATION OF FLUID INCLUSIONS IN SYN... more ... in The Netherlands EXPERIMENTAL DECREPITATION AND RE-EQUILIBRATION OF FLUID INCLUSIONS IN SYNTHETIC QUARTZ ARNAUD PECHER * IRIGM ... Such a re-equilibration, exclusive of true decrepitation phenomena, probably depends on diffusion processes of the ...
The Himalayan Main Central Thrust pile and its quartz-rich tectonites in central Nepal
Tectonophysics, 1981
... Tectonophysics, 78 (1981) 23-50 23 Eisevier Scientific Publishing Company, Amsterdam Printed ... more ... Tectonophysics, 78 (1981) 23-50 23 Eisevier Scientific Publishing Company, Amsterdam Printed in The Netherlands THE HIMALAYAN MAIN CENTRAL THRUST PILE AND ITS QUARTZ-RICH TECTONITES IN CENTRAL NEPAL JEAN-LUC BOUCHEZ and ARNAUD PECHER ...
Au along the Himalayan chain an axis of crystalline rocks has been preserved, made of the Higher ... more Au along the Himalayan chain an axis of crystalline rocks has been preserved, made of the Higher Himalaya crystalline and the crystalline nappes of the Lesser Himalaya. The salient points of the metamorphism, as deduced from data collected in central Himalaya (central Nepal and Kumaun), are: 1. The Higher Himalaya crystalline, also called the Tibetan Slab, displays a polymetamorphic history with a first stage of Barrovian type overprinted by a lower pressure and/or higher temperature type metamorphism. The metamorphism is due to quick and quasi-adiabatic uplift of the Tibetan Slab by transport along an MCT ramp, accompanied by thermal refraction effects in the contact zone between the gneisses and their sedimentary cover. The resulting metamorphic pattern is an upparenf (diachronic) inverse zonation, with the sillimanite zone above the kyanite zone. 2. Conversely, the famous inverted zonation of the Lesser Himalaya is basically a primary pattern, aquired during a one-stage prograde metamorphism. Its origin must be related to the thrusting along the MCT, with heat supplied from the overlying hot Tibetan Slab, as shown by synmetamorphic microstructures and the close geometrical relationships between the metamorphic isograds and the thrust. 3. Thermal equilibrium is reached between units above and below the MCT. Far behind the thrust tip there is good agreement between the maximum temperature attained in the hanging wall and the temperature of the Tibetan Slab during the second metamorphic stage; but closer to the.MCT front, the thermal accordance between both sides of the thrust is due to a retrogressive metamorphic episode in the basal part of the Tibetan Slab.
Exhumation, crustal deformation, and thermal structure of the Nepal Himalaya derived from the inversion of thermochronological and thermobarometric data and modeling of the topography
Himalayas where erosion, resulting of the interplay between climate and tectonics shapes the most... more Himalayas where erosion, resulting of the interplay between climate and tectonics shapes the most spectacular landscapes on the planet. But what about more internal and deepest surface fluid infiltration? Here we report analysis of the δ 18 O (water) and δD (water) of extracted water from fluid inclusions hosted into Cenozoic quartz veins sampled in the core of the Himalayan range, near the Main Central Thrust and the South Tibetan Detachment. Isotopic and microthermometric values suggest a meteoric origin for the fluids trapped in the quartz of syn-to post-kinematic veins formed between 10 to 20 km depth. Moreover, the isotopic compositions obtained in this study on quartz fluid inclusions water collected along a transect across the Himalayan range evolved with the topography in a similar manner than the modern meteoric water. Considering the age of formation of the quartz veins between 18 and 12 Ma, we deduce that the morphology of the Himalayan topographic front was already shaped during the Miocene but located further north.
Journal of South American Earth Sciences, Aug 1, 2017
In subduction settings, the tectonic regime of the overriding plate is closely related to the geo... more In subduction settings, the tectonic regime of the overriding plate is closely related to the geometry of the subducting plate. Flat-slab segments are supposed to increase coupling at the plate interface in the Andes, resulting in an increase and eastward migration of the shortening in the overriding plate. Above the Peruvian flat-slab, a 200 km-long normal fault trend parallel to the range and delimits the western flank of the Cordillera Blanca. In a context of flat subduction, expected to produce shortening, the presence of the Cordillera Blanca normal fault (CBNF) is surprising. We performed a systematic inversion of striated fault planes in the Cordillera Blanca region to better characterize the stress field above the Peruvian flat-slab. It evidences the succession of different tectonic regimes. NE-SW extension is predominant in most of the sites indicating a regional extension. We suggest that the Peruvian flat-slab trigger extension in the Western Cordillera while the shortening migrated eastward. Finally, we propose that flat-slab segments do not increase the coupling at the trench neither the shortening in the overriding plate but only favor shortening migration backward. However, the stress field of the overriding plate arises from the evolution of plate interface properties through time due to bathymetric anomaly migration.
The Sardinia Channel is located in a 400 km-long submerged section of the Apennine-Maghrebian bra... more The Sardinia Channel is located in a 400 km-long submerged section of the Apennine-Maghrebian branch of the Alpine chain. The Sardinia Channel connects the Algerian-Ligurian-Provençal to the Tyrrhenian oceanic basins. The structure of this region results from the superposition of two tectonic regimes: an earlier crustal thickening and a later crustal thinning. The crustal thickening is the consequence of the shortening which occurred in the late Oligocene-early Miocene during the build up of the Apennine-Maghrebian Orogen. This thickening is coeval with the rotation of the Corsican-Sardinian block and the opening of the Provençal-Algerian back-arc basin. All of these structures, as well as the magmatic arcs in Sardinia and Tunisia, i.e. the Galite Archipelago, are connected to the subduction of the Tethyan Ocean. The crustal thinning is associated with the rifting of the Tyrrhenian Basin, which occurred just before the Messinian salinity crisis and was accompanied by significant erosion throughout the region. This erosion was followed by a period of thermal subsidence linked to the opening of the Tyrrhenian oceanic basin in the Plio-Quaternary, interspersed with minor episodes of compression. On the Sardinian margin, the dives led to the discovery of a submarine volcano, dated at 12.6 Ma, and composed of shoshonitic andesites with lamprophyre inclusions, and to the characterization of the nature and structure of the underlying basement, consisting of tilted blocks of Hercynian metamorphic and granitic rocks and their sedimentary cover. The sea floor morphology reflects this structure. The other areas of the Sardinia Channel explored, i.e. its southern margin and central ridge, belong to the Calabrian-Peloritanian-Kabylian group (CPK). They are composed of a metamorphic and granitic Hercynian basement deformed during the Alpine orogeny, which is stratigraphically overlain by an Oligo-Miocene detrital cover of Peloritanian or Kabylian type, and tectonically overlain by the so-called "flysch nappe". Throughout the CPK domain these formations were subjected during the Oligo-Miocene, at ca. 23 Ma ago, to a first denudation event, and during the Tortonian, ca. 10-8 Ma ago, to a second denudation, which has been connected to the opening of the Tyrrhenian basin. Structures, microstructures and thermochronological data indicate relatively low P-T conditions for the extensional deformations: this suggests that these units remained at shallow depths in the Apennine-Maghrebian Orogen, and were relatively preserved from the Messinian erosion. The age (12.5 Ma) and nature of the volcanic sequence in the Sorelles is closely comparable with the calc-alkaline suite of the Galite Archipelago, Tunisia. Thus, the data gathered during the dives in the Sardinia Channel give new constraints to the reconstruction of the kinematic evolution not only of the region, but also to the entire western Mediterranean. Structure du canal de Sardaigne : réamincissement crustal et extension tardi-orogénique au sein de la chaîne Apennino-Maghrébienne ; résultats des campagnes de plongées Cyana SARCYA et SARTUCYA en Méditerranée occidentale Mots clés.-Méditerranée occidentale, Canal de Sardaigne, Exploration en submersible, Evolution géodynamique néogène, Réamincissement crustal. Résumé.-Le canal de Sardaigne est installé sur un segment immergé de la branche Apennino-Maghrébide de la Chaîne alpine long de 400 km ; il assure une communication profonde entre les bassins océaniques Algéro-Liguro-Provençal et Tyrrhénien. Les structures de ce domaine résultent de la superposition de deux régimes tectoniques successifs, d'abord d'épaississement crustal, suivi d'un réamincissement. Ce dernier est associé au rifting Tyrrhénien ; il s'est produit juste avant la crise messinienne ; celle-ci a entraîné une importante érosion de tout le domaine. Une période de subsidence thermique liée à l'ouverture océanique du bassin Tyrrhénien caractérise ensuite le Plio-Quaternaire, pendant lequel se produisent cependant des épisodes mineurs d'inversion.
The postseismic deformation consecutive to the April 25, 2015 Gorkha earthquake (Mw 7.9) is estim... more The postseismic deformation consecutive to the April 25, 2015 Gorkha earthquake (Mw 7.9) is estimated in this paper based on a cGNSS network installed prior to the earthquake and supplemented by 6 cGNSS stations installed after the main shock. Postseismic displacement are obtained from daily time series corrected for interseismic deformation and seasonal variations. The maximum postseismic displacement is found north of the rupture area, where locally it reached 100 mm between the date of the earthquake and late 2016. The postseismic deformation affects the northern part of the rupture area but not the southern part, along the
More than 15 years of field and laboratory investigations on samples from Terre Adélie to the wes... more More than 15 years of field and laboratory investigations on samples from Terre Adélie to the western part of George V th Land (135 to 146°E) during the GEOLETA program allow a reassessment of the Terre Adélie Craton (TAC) geology. The TAC represents the largest exposed fragment of the East Antarctic Shield preserved from both Grenville and Ross tectono-metamorphic events. Therefore it corresponds to a well-preserved continental segment that developed from the Neoarchean to the Paleoproterozoic. Together with the Gawler Craton in South Australia, the TAC is considered as part of the Mawson continent, i.e. a striking piece of the Rodinia Supercontinent. However, this craton represents one of the less studied parts of the East Antarctic Shield. The three maps presented here clearly point out the extent of two distinct domains within the Terre Adélie Craton and suggest that the TAC was built up through a polyphased evolution during the Neoarchean-Siderian (c.a. 2.5Ga) and the Statherian (c.a. 1.7Ga) periods. These data support a complete re-assessment of the TAC geology and represent a valuable base for the understanding of global geodynamics changes during Paleoproterozoic times.
Tectonometamorphic evolution of the central Karakorum (Baltistan, northern Pakistan)
Tectonophysics, 1996
New structural and metamorphic data from the Chogo Lungma glacier area and Basha valley enlighten... more New structural and metamorphic data from the Chogo Lungma glacier area and Basha valley enlighten the polyphased tectonometamorphic evolution of the Metamorphic Complex of Karakorum. A pre- to early D1 event is defined by a metamorphic cleavage in the core of some zoned garnet and staurolite porphyroblasts. The main tectonometamorphic event (D1) is characterized by N110°E south-vergent isoclinal folds associated
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1999
Granite and gneiss have been sampled on the submarine fault scarps of the Sardinia Channel and ha... more Granite and gneiss have been sampled on the submarine fault scarps of the Sardinia Channel and have been dated using the ""ArY3"Ar method. The majority of rocks partially preserve Hercynian ages. Some of them display Lower Cretaceous .lge.s. In addition, Upper Eocene-Oligocene argon resetting is recorded only in rocks from the southeast sector of the Channel. We thus propose that the basement of the Sardinid Channel occupied a shallow position within the stack of the Alpine tectonic units, behind the more deformed front of the internal zones of the Maghrebide Chain. (0 Academic des sciences / Elsevier, Paris.) * Correspondance et tires B part.
The Shyok Suture Zone of the Ladakh palaeovolcanic arc is made of Cretaceous volcanosedimentary f... more The Shyok Suture Zone of the Ladakh palaeovolcanic arc is made of Cretaceous volcanosedimentary formations intruded by granodioritic plutons. Field observations show a tectonic stacking of litho-units from different volcanic arc and back-arc environments. In the western part (Skardu area), the Shyok Suture Zone can be subdivided into two groups: (1) The Northern Group, which consists of olistolith basaltic blocks and tuffs. The basalts are LREE depleted with a LILE enrichment and a slight Nb depletion suggesting a back-arc basin origin. (2) The Southern Group, which consists predominantly of andesites that show LREE enrichment, a flat HREE pattern, strong Nb-Ta depletion, and LILE enrichment. The volcanic rocks of the Southern Group appear to have island-arc tholeiite (IAT) to calc-alkaline affinities. In the eastern part of the suture zone (Nubra-Shyok area), Albian to Cenomanian age silicoclastic sediments predominate. These sediments correspond to a large detrital platform built on the northern part of the Ladakh Arc. At the top, these sediments interlayer with basaltic to andesitic lavas. These lavas appear to be more differentiated and calc-alkaline in nature than the Skardu Southern Group lavas, but show similar volcanic arc affinities. No evidence of a back-arc basin was found in this area. Our data from these two areas shows a northwest-southeast evolution, from back-arc to arc formations in northern Ladakh. Opening of this back-arc basin occurred on the northwestern side of the Ladakh Arc. This back-arc was progressively closing eastward. The arc itself was more mature in the east, resembling the southern Tibetan continental arc, and was characterised by more continental sedimentation. Subsequent Himalayan tectonometamorphic evolution, closure of the back-arc basin and deformation along the Shyok Suture, reflects an early asymmetrical geometry along the Asian margin and Kohistan-Ladakh Arc.
In central Nepal, the Tibetan Slab is made up of biotite-gneisses (metapelites and metagreywackes... more In central Nepal, the Tibetan Slab is made up of biotite-gneisses (metapelites and metagreywackes), orthogneisses (metagranites) and migmatites. Melanosomes are generally biotite-(f muscovite)-bearing, but locally they may be tourmaline-rich when associated with boron-rich granitic material. Leucosomes occur as lenses conformable with the foliation, veins, patches, or as fillings in shear zones and extensional structures. Field relationships, and mineralogical and chemical data show that three processes may have contributed to the formation of the Tibetan Slab leucosomes: metamorphic differentiation or disequilibrium partial melting (low-Zr tonalitic leucosomes), in-situ equilibrium partial melting (high-Zr leucosomes and some granitic leucosomes) and injection of externally-derived melts (most granitic and some tonalitic leucosomes). The Manaslu pluton belongs to the High Himalayan leucogranite belt and was emplaced at the top of the Tibetan Slab. It corresponds to a muscovite-biotite leucogranite that has been assumed to derive from melting of the Tibetan Slab gneisses (Formation I). Phase relationships, a more magnesian chemistry of the ferromagnesian minerals from the Tibetan-Slab migmatites as compared to the Manaslu leucogranite, the microtextures of accessory phases, and trace-element compositions (lower U, Li, F and higher Sr, Eu, Y, Yb contents in the migmatite leucosomes) show that the in situ Himalayan migmatites, at the crustal level presently exposed, have not been produced under the same P-T-X,Io conditions as the Manaslu leucogranite magma. While the Formation I was the probable source for the Manaslu granite, migmatites within the formation are not the remanants of a melting process from which the Manaslu granite was derived. Both the Tibetan Slab migmatites and the Manaslu leucogranite may be considered as evidence of dehydration and melting at deeper crustal levels, and of percolation of melts and hydrothermal fluids through the crust.
Kashmir earthquake ruptured an out-of-sequence Himalayan thrust known as the Balakot-Bagh thrust.... more Kashmir earthquake ruptured an out-of-sequence Himalayan thrust known as the Balakot-Bagh thrust. The earthquake's hypocenter was located at a depth of 15 km on the ramp close to a possible ramp/flat transition. In the weeks following the earthquake a GPS network was installed to measure postseismic displacement. The initial measurements in November 2005 were followed by other campaigns in January and
Evolution à pression et température élevées d'inclusions fluides dans un quartz synthétique
Bulletin de Minéralogie, 1984
Des echantillons d'un monocristal de quartz synthetique contenant des inclusions fluides (I.F... more Des echantillons d'un monocristal de quartz synthetique contenant des inclusions fluides (I.F.) ont ete chauffes dans un autoclave (T = 448 °C, correspondant a une pression interne Pi de 282 MPa dans les inclusions). La pression d'argon de confinement etait soit inferieure (Pc = 200 MPa, duree 69 a 3 064 h) soit superieure (Pc = 350 MPa, duree 2 086 h) a Pi. La comparaison des I.F. avant et apres experience montre qu'elles ont subi des changements importants de forme et des variations mesurables de la densite. Deux processus d'evolution sont observes et discutes : — Reequilibrage rapide par decrepitation et apparition d'I.F. secondaires. La forte diminution de la densite des inclusions s'explique par l'augmentation de volume de la cavite lors de la decrepitation. Un nouvel equilibre tel que Pi ⋍ Pc est indique par les mesures de Th. — Les I.F. non decrepitees montrent une evolution progressive de leurs forme et densite. Des formes en cristaux negatifs sont rapidement atteintes et leur rapport L/l decroit jusqu'a une valeur limite de 3 environ. Quand Pi est superieure a Pc, Th augmente progressivement avec le temps (Δ Th atteignant 10 °C, c'est-a-dire une diminution de la densite de 0,015). Une diffusion d'OH- et une rehydratation du quartz hote sont proposees comme explication possible de la diminution de la densite. Quand Pi est inferieure a Pc, la densite des I.F. augmente et ce phenomene reste encore inexplique.
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1997
Two new occurrences of HP rocks have been found in the Indus suture zone on the eastern side of t... more Two new occurrences of HP rocks have been found in the Indus suture zone on the eastern side of the Nanga Parbat-Haramosh massif: a retrogressed eclogitic assemblage in pyroxenitic boudins within the Iadakh island-arc sequence, and an HP granulitic paragenesis in mafic alternations of High Himalaya banded gneisses. PT estimates on five samples with garnet-clinopyroxene-amphiboleplagioclase-quartz-FeTi oxide-biotite mineral assemblage have respectively yielded 13 + 1 kbar for 610 rt 30 OC, and 10 f 1 kbar for 700 & 50 'C. This metamorphism is linked to the continuous subduction of continental and arc material after India-Eurasia collision. The granulitic retrogression corresponds to a phase of collage, with prograde granulites during exhumation.
This paper presents TrackDip, a new method for dipmeter data processing. This method selects, loc... more This paper presents TrackDip, a new method for dipmeter data processing. This method selects, localizes and measures significant tilts from the comparison at various scales of the changes of orientation of sedimentary beddings. We tested this method on simple cases (unconformity, gradual tilt, successive tilts, without and with additional random noise) and on a field example, along three sections in the Eocene Sobrarbe delta, Ainsa foreland basin, northern Spain. For synthetic data sets, the method clearly identifies and measures the introduced tilts. On the field, sedimentary and tectonic structures, especially three main syn-sedimentary sliding surfaces (S1 to S3), were successfully identified from processed dipmeter data. The tilt axis are mainly trending N-S in sandstones, associated to westward transport of sediments. The sliding surfaces S1 and S3 correspond to E-W-trending tilt axis, tentatively correlated either to the flexural subsidence of the basin, or to anticline growth during sedimentation south of the studied area. Combination of these sedimentary and tectonic directions results in a NE-SW striking submarine slope, which locally controls the gravitydriven deformations, especially on the S2 sliding surface. Finally, NNW-SSE-trending tilts above the uppermost S3 sliding surface are interpreted as the result of infilling on the side of the scar produced by sliding.
Metamorphic and Magmatic Evidences fo Neogenous Slab Breakoff Beneath S-Karakorum and S-Tibet
On the S- Karakorum margin, Neogene granulites define an east-west trending thermal anomaly. Thes... more On the S- Karakorum margin, Neogene granulites define an east-west trending thermal anomaly. These rocks have been heated from 600 to 750° C during a slight pressure drop, from 0.7 to 0.5 GPa. Their retrogressive path cross-cuts the relaxed geotherm of tectonically thickened crust. Such a P-T evolution can be obtained only if an advective source of heat is involved.
Slow steady exhumation of the high elevation Deosai Plateau (Northern Pakistan Himalaya) since 40 Ma
Mountain ranges of the north-western Himalaya in Pakistan show strongly contrasting relief, oppos... more Mountain ranges of the north-western Himalaya in Pakistan show strongly contrasting relief, opposing steep, deeply incised topography with extremely high peaks such as the Karakorum Range and Nanga Parbat Haramosh Massif (NPHM), to high-altitude, low-relief areas such as the Deosai Plateau located between the Karakorum and NPHM and the Tso-Morari Massif in Eastern Ladakh. In contrast, mean elevations of the
Experimental decrepitation and re-equilibration of fluid inclusions in synthetic quartz
Tectonophysics, 1981
... in The Netherlands EXPERIMENTAL DECREPITATION AND RE-EQUILIBRATION OF FLUID INCLUSIONS IN SYN... more ... in The Netherlands EXPERIMENTAL DECREPITATION AND RE-EQUILIBRATION OF FLUID INCLUSIONS IN SYNTHETIC QUARTZ ARNAUD PECHER * IRIGM ... Such a re-equilibration, exclusive of true decrepitation phenomena, probably depends on diffusion processes of the ...
The Himalayan Main Central Thrust pile and its quartz-rich tectonites in central Nepal
Tectonophysics, 1981
... Tectonophysics, 78 (1981) 23-50 23 Eisevier Scientific Publishing Company, Amsterdam Printed ... more ... Tectonophysics, 78 (1981) 23-50 23 Eisevier Scientific Publishing Company, Amsterdam Printed in The Netherlands THE HIMALAYAN MAIN CENTRAL THRUST PILE AND ITS QUARTZ-RICH TECTONITES IN CENTRAL NEPAL JEAN-LUC BOUCHEZ and ARNAUD PECHER ...
Au along the Himalayan chain an axis of crystalline rocks has been preserved, made of the Higher ... more Au along the Himalayan chain an axis of crystalline rocks has been preserved, made of the Higher Himalaya crystalline and the crystalline nappes of the Lesser Himalaya. The salient points of the metamorphism, as deduced from data collected in central Himalaya (central Nepal and Kumaun), are: 1. The Higher Himalaya crystalline, also called the Tibetan Slab, displays a polymetamorphic history with a first stage of Barrovian type overprinted by a lower pressure and/or higher temperature type metamorphism. The metamorphism is due to quick and quasi-adiabatic uplift of the Tibetan Slab by transport along an MCT ramp, accompanied by thermal refraction effects in the contact zone between the gneisses and their sedimentary cover. The resulting metamorphic pattern is an upparenf (diachronic) inverse zonation, with the sillimanite zone above the kyanite zone. 2. Conversely, the famous inverted zonation of the Lesser Himalaya is basically a primary pattern, aquired during a one-stage prograde metamorphism. Its origin must be related to the thrusting along the MCT, with heat supplied from the overlying hot Tibetan Slab, as shown by synmetamorphic microstructures and the close geometrical relationships between the metamorphic isograds and the thrust. 3. Thermal equilibrium is reached between units above and below the MCT. Far behind the thrust tip there is good agreement between the maximum temperature attained in the hanging wall and the temperature of the Tibetan Slab during the second metamorphic stage; but closer to the.MCT front, the thermal accordance between both sides of the thrust is due to a retrogressive metamorphic episode in the basal part of the Tibetan Slab.
Exhumation, crustal deformation, and thermal structure of the Nepal Himalaya derived from the inversion of thermochronological and thermobarometric data and modeling of the topography
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