Éditeur(s) : HAL CCSD
Résumé : International audience
Understand the dynamics of the fresh-salt water interface in aquifers is a key issue to comprehend mixing processand to quantity the discharge of nutrients in to coastal areas. In order to go beyond the current knowledge inthis issue an experimental site has been set up at the alluvial aquifer Riera Argentona (Barcelona – Spain). Thesite comprises 16 shallow piezometers installed between 30 and 90 m from the seashore, with depths rangingbetween 15 and 25 meters. The seawater interface is being monitored using several techniques, the combinationof which will help us to understand the spatial and temporal behaviour of the mixing zone and the geochemicalprocesses occurring there. Specially the deepest piezometers are equipped with electrodes in order to performcross-hole electrical resistivity tomography (CHERT). In addition, all piezometers are also equipped with FiberOptic cable to perform distributed temperature measurements. Two single steel armoured fibre optic cable lines ofaround 600m length were installed in all boreholes. The objective is to use the cable both as passive and activetemperature sensor. The first is being done for the continuous monitoring of temperature whereas; the secondprovides a higher temperature resolution used to monitor field experiments.Periodic CHERT measurements are carried out between the piezometer equipped with electrodes, resultingin parallel and perpendicular vertical cross sections of the site resistivity. The position of the fresh-salt waterinterface can be identified due to the resistivity contrast between the saline and fresh water. Preliminary resultsof periodic distributed temperature measurements will be also be used to monitor the position of the mixing zonethanks to the contrast and seasonal temperature changes. Periodic down-hole EC profiles will be used to validatethe method.AcknowledgementsThis work was funded by the projects CGL2013-48869-C2-1 y CGL2013-48869-C2-2-R of the Spanish Government.We would like to thank SIMMAR (Serveis Integrals de Manteniment del Maresme) and the ConsellComarcal del Maresme in the construction of the research site
European Geosciences Union General Assembly 2016
Vienne, Austria

insu-01308757
https://hal-insu.archives-ouvertes.fr/insu-01308757

Éditeur(s) : HAL CCSD
Résumé : International audience
The geology of the North Pyrenean Zone in the central Pyrenees allows for the observation in the field of theentire section of the Pyrenean rift, from the mantle to the crust and the Mesozoic cover (pre, syn and post rift).The good knowledge we have of the pre-Alpine history of the Pyrenees allows us to properly constrain the Alpinegeological evolution of the pre-Triassic rocks which record both Variscan and Alpine orogenic cycles.The mantle outcrop as kilometric to centimetric fragments of peridotite dispersed within a carbonate metamorphicbreccia. The study of peridotite serpentinisation shows several events of low-temperature serpentinisation, incontact with seawater. In some locallities, we can observe a mixture of fragments of variously serpentinizedperidotites. This suggests a tectonic context where fragments of peridotites from different structural levels weresampled more or less synchronously.The granulitic basement is characterized by a Variscan syndeformational HT event (300-280 Ma). So farwe have not found any trace of a Cretaceous HT event (> 500C). On the other hand, the basement is affectedby a regional metasomatism that began during the Jurassic and became more spatially focused with time until itwas restricted to the Pyrenean rift during the Aptien, Albian and Cenomanian. The talc-chlorite metasomatism(120-95 Ma) shows an evolution from a static toward a syn-deformation hydrothermal event, under a more or lessnormal geothermal gradient. Extensional deformation is recorded by the reworking of several inherited low-angleVariscan tectonic contacts, but also by dispersed high-angle extensional shear zones formed under greenshistconditions.The metamorphic Mesozoic cover of the basement massifs, which constitute the so-called Internal MetamorphicZone, is an allochtonous unit made of lenses of Mesozoic rocks enclosed into the breccia, whichlocally contains peridotite and basement clasts. The Mesozoic metamorphic carbonates show a first phase ofsyn-metamorphic (450-600C, P < 2 kb) ductile deformation, and subsequent phases of folding and fracturing.The datation of neoformed minerals give a 108-85 Ma time span for the metamorphism. We interpret this brecciaas an abandonment breccia which marks the emergence of the main detachment. The basal contact of the Mesozoiccover has a complex 3D geometry traced by Triassic evaporites. It corresponds to a major pre- and synorogenicpolyphased tectonic contact.All these data show a geometrically complex hyper-extended rift where the crust was not stretched under ahigh geothermal gradient but thinned by the tectonic extraction of relatively thin lenses and perhaps cut by highangle low-grade shear zones. The 3D geometry, as well as the strain records and the breccia lithologies stronglysuggest a non-cylindricity for the exhumation process, probably within a transtentional system
Geophysical Research Abstracts
Vienne, Austria

insu-01510371
https://hal-insu.archives-ouvertes.fr/insu-01510371

Éditeur(s) : HAL CCSD
Résumé : International audience
Metamorphic soles correspond to m to 500m thick tectonic slices welded beneath most of the large-scale ophiolites.They typically show a steep inverted metamorphic structure where the pressure and temperature conditions ofcrystallization increase upward (from 500100ºC at 0.50.2 GPa to 800100ºC at 1.00.2 GPa), with isogradssubparallel to the contact with the overlying ophiolitic peridotite. The proportion of mafic rocks in metamorphicsoles also increases from the bottom (meta-sediments rich) to the top (approaching the ophiolite peridotites). Thesesoles are interpreted as the result of heat transfer from the incipient mantle wedge toward the nascent slab (associatedwith large-scale fluid transfer and possible shear heating) during the first My of intra-oceanic subduction(as indicated by radiometric ages). Metamorphic soles provide therefore major constraints on early subductiondynamics (i.e. thermal structure, fluid migration and rheology along the nascent slab interface).We present a detailed structural and petrological study of the metamorphic sole from 4 major cross-sections alongthe Oman ophiolite. We show precise pressure–temperature estimates obtained by pseudosection modelling andEBSD measurements performed on both the garnet-bearing and garnet-free high-grade sole. Results allow quantificationof the micro-scale deformation and highlight differences in pressure–temperature–deformation conditionsbetween the 4 different locations, showing that the inverted metamorphic gradient through the sole is not continuousin all locations.Based on these new constraints, we suggest a new tectonic–petrological model for the formation of metamorphicsoles below ophiolites. This model involves the stacking of several homogeneous slivers of oceanic crust leadingto the present-day structure of the sole. In this view, these thrusts are the result of rheological contrasts between thesole and the peridotite as the plate interface progressively cools down. These slivers later underwent several stagesof retrogression (partly mediated by ascending fluids from the slab) from amphibolite- to prehnite/pumpellite-faciesconditions.
Geophysical Research Abstracts
Vienne, Austria

insu-01309369
https://hal-insu.archives-ouvertes.fr/insu-01309369

Éditeur(s) : HAL CCSD
Résumé : International audience
The deformation of natural systems in response to subsurface water storage and redistribution provides insightsinto the main water flow path within heterogeneous systems, including the role of faults or fractures. A longbaseline tiltmeter was installed in the low-noise underground laboratory of Rustrel (LSBB) to study the responseof the Fontaine de Vaucluse (FDV) karst hydrosystem to water cycle. Tilt data and piezometric levels recorded in aborehole close to the LSBB show a strong correlation with the discharge of the system observed at the FDV spring30 km away. Over several months, tilt data were recorded on three base lines, thus allowing, for the first time,to study the tilt gradient variation that appears homogeneous. Such information provides a significant constrainton hydrological processes leading to the measured deformation. Several deformation models were tested usingthe ADELI code to estimate the type of hydro-mechanical structure that could reproduce the measured tilt andits gradient. On one hand, models show that uniform loading at the surface produces a much smaller signal thanobserved on measured data. On the other hand, the deformation related to the filling of a fracture following aprecipitation event requires unrealistic fracture size. Finally, we found that a suitable hydro-mechanical modelcorresponds to the loading of numerous fractures at the interface between the saturated and unsaturated zones. Sucha configuration predicts a tilt distribution in agreement with observations. This study suggests that tilt networksinto a karst system should provide key observation for deciphering hydrological processes
Geophysical Research Abstracts
Vienne, Austria

insu-01308594
https://hal-insu.archives-ouvertes.fr/insu-01308594

Éditeur(s) : HAL CCSD
Résumé : International audience
Understanding subduction rheology in both space and time has been a challenge since the advent of plate tectonics.We herein focus on "subduction infancy", which corresponds to the first 0-2 My immediately following subductionnucleation, when a newly born slab penetrates into the overriding plate mantle and heats up.The only remnants of this critical, yet elusive, geodynamic step are thin metamorphic soles, commonly found beneathpristine, 100-1000 km long portions of oceanic lithosphere emplaced on top of continents (i.e. ophiolites).In this study, we show how, during subduction infancy, transient mechanical properties of both the mantle and crustacross the subduction plate interface (during 100s ky) control and hinder the penetration of tectonic plates intothe mantle, and how this results in strong peaks of resistance and even slicing of their surface — leaving behindthin, chopped-off metamorphic slivers (i.e. metamorphic soles).These findings constrain the mechanical behaviour of the subduction plate interface (with implications for couplingprocesses and earthquake generation) as well as the properties of the crust and mantle. They also highlight the roleof fluids in enabling subduction to overcome this early resistance.
Geophysical Research Abstracts
Vienne, Austria

insu-01309386
https://hal-insu.archives-ouvertes.fr/insu-01309386

Éditeur(s) : HAL CCSD
Résumé : International audience
Aegean extension is a process driven by slab rollback that since 45 Ma shows a two-stage evolution. From 45 to13 Ma it is accommodated by localized deformation leading to i) the exhumation of high-pressure metamorphicrocks from mantle to crustal depths, ii) the exhumation of high-temperature rocks in core complexes and iii) thedeposition of Paleogene sedimentary basins. Since 13 Ma, extension is distributed over the whole Aegean domaingiving a widespread development of onshore and offshore Neogene sedimentary basins. The 3D reconstruction atAegean scale of this two-stage evolution shows that the rate of trench retreat was around 0.6 cm/y during the first30 My and then accelerated up to 3.2 cm/y during the last 13 My. Using available tomographic evidence, timingof metamorphic and sedimentary processes, paleomagnetic data and geometry and kinematics of deformation, wepropose that the sharp transition in trench retreat and deformation mode, localized vs distributed, at 13 Ma wascontrolled to slab tearing. Moreover, the development of dextral NE-SW strike-slip faults and related pull-apartbasins in the North Aegean domain, from the Cyclades to the Rhodope, strongly suggests that this sharp transitionalso corresponds to the onset of Anatolia westward escape.
Geophysical Research Abstracts
Vienne, Austria

insu-01137631
https://hal-insu.archives-ouvertes.fr/insu-01137631

Éditeur(s) : HAL CCSD
Résumé : International audience
The core of South East Asia is composed of a mosaic of continental blocks, among which the Indochina and theSouth China blocks (present day northern Vietnam), amalgamated during the Permian and/or the Triassic. LatePermian to Late Triassic geodynamic evolution of these two blocks remains controversial. The main discussionpoints concern the existence and the closure of an oceanic domain separating the Indochina and the South Chinablocks during this period. Especially, the polarity and the timing of the subduction zone that led to the collisionbetween the blocks as well as the present location of the suture delimiting them are a matter of debate. Despite thevaluable information they can provide, the sedimentary basins from northern Vietnam have been neglected in theprevious studies dealing with the geodynamic evolution of South East Asia.To determine the geodynamic evolution of the area, the basins of Sam Nua and Song Da, presently locatedin North Vietnam, have been investigated using a combined approach involving sedimentology, geochronology(U-Pb/zircon) and geochemistry (whole-rock major and trace elements composition of both volcanic and volcaniclasticrocks). The palaeoenvironment evolution, the main unconformities, their age and the tectonic affinitiesof the interbedded volcanic and volcaniclastics series have been characterized for these two basins. Our resultsdemonstrate (i) that the Song Da Basin exhibits a palaeogeographic affinity with the South China block, (ii) theoccurrence of extensive calk-alkaline volcanism and associated volcaniclastic deposits in the Sam Nua Basin,related to the existence of an active magmatic arc during the Early and the lower Middle Triassic, (iii) a Southdipping (present day coordinate) oceanic lithosphere beneath the Indochina block, deduced from the location ofthe magmatic arc south of the potential suture zones, (iv) that an angular unconformity postdates the lower MiddleTriassic volcaniclastic deposits in the Sam Nua basin. This unconformity, crosscutting the subduction relateddeposits, is interpreted as the result of the collision between the Indochina and the South China blocks.
European Geoscience Union General Assembly 2015
Vienne, Austria

insu-01137675
https://hal-insu.archives-ouvertes.fr/insu-01137675

Éditeur(s) : HAL CCSD
Résumé : International audience
Metamorphic soles correspond to m to 500 m thick highly strained metamorphic rock units found beneath myloniticbanded peridotites at the base of large-scale ophiolites, as exemplified in Oman. Metamorphic soles aremainly composed of metabasalts deriving from the downgoing oceanic lithosphere and metamorphosed up togranulite-facies conditions by heat transfer from the mantle wedge. Pressure–temperature peak conditions areusually estimated at 1.00.2 GPa and 800100ºC. The absence of HP–LT metamorphism overprint implies thatmetamorphic soles have been formed and exhumed during subduction infancy. In this view, metamorphic soleswere strongly deformed during their accretion to the mantle wedge (corresponding, now, to the base of the ophiolite).Therefore, metamorphic soles and banded peridotites are direct witnesses of the dynamics of early subductionzones, in terms of thermal structure, fluid migration and rheology evolution across the nascent slab interface.Based on fieldwork and EBSD analyses, we present a detailed (micro–) structural study performed on samplescoming from the Sumeini window, the better-preserved cross-section of the metamorphic sole of Oman. Largedifferences are found in the deformation (CPO, grain size, aspect ratio) of clinopyroxene, amphibole and plagioclase,related to mineralogical changes linked with the distance to the peridotite contact (e.g., hardening due to theappearance of garnet and clinopyroxene).To model the incipient slab interface in laboratory, we carried out 5 hydrostatic annealing and simple-shear experimentson Griggs solid-medium apparatus. Deformation experiments were conducted at axial strain rates of 10-6s-1. Fine-grained amphibolite was synthetized by adding 1 wt.% water to a (Mid-Ocean Ridge) basalt powder asa proxy for the metamorphic sole (amphibole + plagioclase + clinopyroxene garnet assemblage). To synthetizegarnet, 2 experiments were carried out in hydrostatic conditions and with deformation at 800C with confiningpressure of 2 GPa. Another simple-shear experiment has been carried out at 800C and 1 GPa with fined-grainednatural garnet. With the aim of mimicking the early slab interface (between the metamorphic sole and bandedperidotites at the base of the ophiolite), 2 simple-shear deformation experiments with 2 layers have been carriedout at 800C and confining pressure of 1 GPa. The bottom layer was made of hydrated basalt powder and the toplayer was made of olivine.Fined-grained garnet-free amphibolite is significantly weaker than dunite but the appearance of harder mineralsin the amphibolite (garnet and clinopyroxene) has major implications on its rheological evolution. These resultsallow liking field observations of strain localization at the interface to the metamorphic sole formation
European Geosciences Union General Assembly 2016
Vienne, Austria

insu-01309394
https://hal-insu.archives-ouvertes.fr/insu-01309394

Éditeur(s) : HAL CCSD
Résumé : International audience
Sub-continental lithospheric mantle rocks are exhumed at the foot of magma-poor distal passive margins as aresponse to extreme stretching of the continental crust during plate separation. Remnants of the Northern Iberianpaleo-passive margin are now exposed in the North-Pyrenean Zone (NPZ) and represent field analogues to studythe processes of continental crust thinning and subcontinental mantle exhumation. The NPZ results from theinversion of basins opened between the Iberia and Europa plates during Albo-Cenomanian times. In the westernNPZ, the ‘Chaînons Béarnais’ ranges display a fold-and-thrust structure involving the Mesozoic sedimentarycover, decoupled from its continental basement and associated with peridotite bodies in tectonic contact withPalaeozoic basement lenses of small size. Continental extension developed under hot thermal conditions, asdemonstrated by the syn-metamorphic Cretaceous ductile deformation affecting both the crustal basement and theallochthonous Mesozoic cover.In this study, we present structural and geochemical data providing constraints to reconstruct the evolution ofthe northern Iberia paleo-margin. Field work confirms that the pre-rift Mesozoic cover is intimately associatedto mantle rocks and to thin tectonic lenses of crustal basement. It also shows that the pre-rift cover was detachedfrom its bedrock at the Keuper evaporites level and was welded to mantle rocks during their exhumation atthe foot of the hyper-extended margin. The crust/mantle detachment fault is a major shear zone characterizedby anastomosed shear bands defining a plurimetric phacoidal fabric at the top of the serpentinized mantle. Thedetachment is marked by a layer of metasomatic rocks, locally 20 meters thick, made of talc-chlorite-pyrite-richrocks that developped under greenschist facies conditions. Raman Spectroscopy on Carbonaceous Materials(RSCM), performed on the Mesozoic cover reveal that the entire sedimentary pile underwent temperatures rangingbetween 200C and 480C.We show that: (i) at the site of mantle rocks exhumation, the boudinaged pre-rift sediments have undergone drasticsyn-metamorphic thinning with the genesis of a S0/S1 foliation and, (ii) the Paleozoic basement has been ductilelydeformed, into thin tectonic lenses that remained welded to the exhumed mantle rocks. Therefore the overallcrustal rheology appears dominated by shallow levels having a ductile behavior. This rheology is related to thepresence of a thick pre- and syn-rift decoupled cover acting as an efficient thermal blanket. This new geologicaldata set highlights important characteristics of ductile-type hyper-extended passive margin that cannot be obtainedfrom the study of seismic lines. Finally, we stress that studying field analogues represents a major tool to betterunderstand the mechanisms of extreme crustal thinning associated with mantle exhumation and their structuralinheritance during tectonic inversion.
Geophysical Research Abstracts
Vienne, Austria

insu-01510103
https://hal-insu.archives-ouvertes.fr/insu-01510103

Éditeur(s) : HAL CCSD
Résumé : International audience
After the 2009 Morakot typhoon, which triggered numerous large landslides in Taiwan, Mouyen et al. (2013)showed for the first time the potential of time-lapse gravity survey to infer the mass of sediments transferringby landsliding or through rivers. By providing an integrated measurement of masses, gravimetry might thus becomplementary to common methods used to assess the sediments discharge of rivers. But the masses of rocksdisplaced by Morakot were exceptionally large as a result of the record-breaking rainfalls brought by this typhoonand one might wonder to what extent time-lapse gravimetry could record such sediment transfers. In order tobetter assess the capabilities of this method, we set a time-lapse gravity network dedicated to the monitoring ofsuch sediments transfers in Paolai village (south-central Taiwan). Paolai is located near the large Laonong riverwhere temporary alluvial deposits of sediments exist and face steep mountain slopes likely to experience landslides.Both features are considered as potential source of mass transfers, and in turn of temporal gravity changes. Thefirst base gravity measurements were done in November 2015, using absolute and relative gravimeters, and will berepeated every year, before and after the typhoon season. In the same time, we also use a terrestrial lidar to scan thegeometry of both the river and the mountain slopes, hence providing a detailed topographical survey of the studiedarea. Adding Lidar measurements is an efficient strategy to solve for the non-uniqueness of gravity solutions.Meanwhile, we use the Eros morphodynamic model, that combine landsliding and flooding models, to investigatevarious scenarios of landsliding and subsequent sediment transport and compute the gravity changes on a virtualnetwork of gravimeters. This gives us insights on the expected order of magnitudes for these surface sedimenttransfers, which are useful to unravel the induced gravity signal from others sources such as local hydrology orvertical ground displacements. The modeling results also enable us to set network location that are best defined todetect mass changes associated with sediment transfer. The main objective of this study is to test whether timelapsegravity brings a new and reliable information compared to present methods monitoring sediments transfersand landscape evolution.
European Geosciences Union General Assembly 2016
Vienne, Austria

insu-01308554
https://hal-insu.archives-ouvertes.fr/insu-01308554

Éditeur(s) : HAL CCSD
Résumé : International audience
Sedimentary basins, through the sedimentary successions and the nature of the deposits, reflect the geology of thearea from which the sediments were derived and thus provide valuable record of hinterland tectonism. As the collisionbetween the South China and the Indochina blocks (i.e. the Indosinian orogeny) is still the object of a numberof controversies regarding, for instance, its timing and the polarity of the subduction, the sedimentary basins associatedwith this mountain belt are likely to provide clues to reconstruct its geodynamic evolution. However, boththe Sam Nua Basin (located to the south of the inner zones of the Indosinian orogeny and the Song Ma ophiolites)and the Song Da Basin (located to the north of the inner zones), northern Vietnam, are still lacking importantinformation regarding the depositional environments and the ages of the main formations that they contain.Using sedimentological and dating analyses (foraminifers biostratigraphy and U-Pb dating on detrital zircon), weprovide a new stratigraphic framework for these basins and propose a geodynamic evolution of the present-daynorthern Vietnam.During the Early Triassic, the Sam Nua Basin was mainly supplied by volcaniclastic sediments originating froman active volcanic activity. Geochemical investigations, combined with sedimentological and structural analyses,support an arc-related setting for this magmatism. This magmatic arc resulted from the subduction of a south dippingoceanic slab that once separated the South China from the Indochina blocks. During the Middle to the LateTriassic, the Sam Nua Basin underwent erosion that lead to the formation of a major unconformity, termed theIndosinian unconformity. This unconformity is interpreted to result from the erosion of the Indosinian mountainbelt, built after the continental collision between the South China and the Indochina blocks. Later, during the LateTriassic, the Sam Nua Basin experienced the deposition of very coarse material, emplaced under continental settingand representing the product of the erosion of the Indosinian mountain belt.To the North, the Song Da Basin is characterized by strongly diachronous deposits over a basal unconformitydeveloped at the expense of volcanic and volcaniclastic deposits related to the Emeishan Large Igneous Province.The sedimentary succession indicates a foreland setting during the Early to the Middle Triassic, which contrastswith the commonly assumed rift setting for these sediments. Thus, the Song Da Basin documents the formation ofthe Indosinian thrust belt, located immediately to the South of the basin.
European Geosciences Union General Assembly 2017
Vienne, Austria

insu-01510331
https://hal-insu.archives-ouvertes.fr/insu-01510331

Éditeur(s) : HAL CCSD
Résumé : International audience
The Alboran Domain, situated at the western end of the Mediterranean subduction system, is characterized by theRonda Peridotites, one of the world largest exposures of sub-continental mantle. Using U-Pb (LA-ICP-MS) and Ar-Ar dating, we precisely dated two tectonic events associated with the Tertiary exhumation of the Ronda Peridotites.First, shearing along the Crust-Mantle Extensional Shear Zone caused, at ca. 22.5 Ma, mantle exhumation, localpartial melting in the deep crust and coeval cooling in the upper crust. Second, the Ronda Peridotites Thrusttriggered the final crustal emplacement of the peridotites onto the continental crust at ca. 21 Ma, as testified bygranitic intrusions in the thrust hanging-wall. The tectonic evolution of the western Alboran Domain is thereforecharacterized by a fast switch from a continental lithosphere extension in a backarc setting, with sub-continentalmantle exhumation, to a rift inversion by thrusting driven by shortening of the subduction upper plate
European Geosciences Union General Assembly 2017
Vienne, Austria

insu-01510393
https://hal-insu.archives-ouvertes.fr/insu-01510393

Éditeur(s) : HAL CCSD
Résumé : International audience
At the time of the collision with India (55Ma), the southern margin of Asia was a composite continental domainresulting from an already long history of successive accretions of different terranes having different rheologies.Knowledge about the structure, composition and thermal state of the Tibetan lithosphere through time is thusfundamental to understand the respective contributions of pre-Cenozoïc and Cenozoïc tectonics in the building ofthe Plateau to its present-day elevations.We focused on the boundary between the Qiangtang terrane to the south, and the Songpan-Ganze terrane to thenorth.We jointly studied deep crustal xenoliths and associated (ultra-)potassic magmatism from the Eocene basinsof Nangqian and Xialaxiu (Qinghai Province, China), north of the Qiangtang terrane. The aims were to retrievethe composition and the thermal state of the lower crust during Eocene times, to study the behavior of the lowercrust and lithospheric mantle of the Eastern Qiangtang terrane and the adjacent Songpan-Ganze terrane at the timeof the collision, and the link with the magmatic activity.Crustal xenoliths are of two types: biotite-rich, amphibole bearing metasediments; and garnet-bearing quartzofeldspathicgneisses. Such assemblages are typical of very high-grade amphibolite and granulite faciesmetamorphism; further study should allow us to quantify the pressures and temperatures those rocks experienceduntil the time they were sampled by their host lavas.Major element geochemistry places the c.a. 51-49 Ma (Spurlin et al., 2005) Xialaxiu volcanic field in a fairlydifferentiated (SiO265-70 wt%) high-K field of the calc-alcaline series. Trace element analysis suggests a strongcrustal contamination of the primary mantellic melts. C.a. 38-37 Ma (Spurlin et al., 2005) Nangqian magmaticbodies span across the alkaline series, with high to extreme (K2O6wt%) values. Complex major and traceelement patterns, coupled with high-resolution microprobe data on pyroxene xenocrysts, suggest that enrichmentoccurred at the source by metasomatism of the lithospheric mantle.Further work will precise which mechanisms could have accounted for such a metasomatism of the mantle beneaththe Northern Qiangtang terrane during Eocene, and whether the lower crust had an autochtonous or allochtonousnature.
Geophysical Research Abstracts
Vienne, Austria

insu-01308919
https://hal-insu.archives-ouvertes.fr/insu-01308919