Papers by Christian Nicollet
Comptes Rendus De L Academie Des Sciences Serie 2 Mecanique Physique Chimie Sciences De L Univers Sciences De La Terre, 1993
Canadian Journal of Earth Sciences, 1978
Egu General Assembly Conference Abstracts, May 1, 2010
Queyras units and Viso unit (Western Alps) are evidence of the Alpin Ocean constituted by pods of... more Queyras units and Viso unit (Western Alps) are evidence of the Alpin Ocean constituted by pods of metagabbros/eclogite associated to a majority of Schistes Lustrés, oficalcits and serpentinite. This study presents detailed petrology of the metagabbro/eclogite constituted these units and thermobarometric datas using pseudosection modelling (PERPLEX) and RSCM thermometer on the Schistes Lustrés (SL) surrounding the metagabbro/eclogite pods. All over the world, lawsonite assemblages are predicted in a broad PT field but are rare in blueschist and eclogite because its stability required high water content. However, the lawsonite blueschist facies is present in the most Queyras units which make of this domain a privileged locality to study the stability between lawsonite and zoisite. Despite the well preserved gabbroic texture of the Queyras blueschist, two types of well equilibrated HP-LT parageneses can be found: (1) lawsonite-glaucophane-omphacite-sphene or (2) zoisite-albite-omphacite-glaucophane-pumpelleyite. Pseudosection calculations reveal the link between the H2O content of the rock and the presence of these two types of parageneses. Moreover the present study shows that zoisite can appear, at the expense of lawsonite, in 2 different cases through the unit: (1) in H2O-undersaturated conditions and (2) in isothermal exhumation conditions. In fact the presence of zoisite in the metagabbro paragenese of the samples studied here, are not due to a temperature effect as commonly believed. PT estimates using pseudosection modelling on metagabbros seems quiet homogeneous through the sample locations. On the other hand, the RSCM results on the schistes lustres lithology show a weak increase of temperature from the west to the east part of the Queyras units. Thus, we discuss the apparent homogeneity of our PT results through the Queyras unit, and the presence or not of a gradient through this unit as it is commonly describe further north in the Schistes Lustrés unit. This present work compares also the PT homogeneities of our results through the southern part of the Queyras unit to the different PT heterogeneities found in Viso unit following the rock type and their locations.
Comptes Rendus De L Academie Des Sciences Serie 2 Sciences De La Terre Et Des Planetes, 1995
... Roche métamorphique. ; Gabbro. ; Roche ignée. ; Mots-clés espagnols / Spanish Keywords. Madag... more ... Roche métamorphique. ; Gabbro. ; Roche ignée. ; Mots-clés espagnols / Spanish Keywords. Madagascar. ; Imaginería. ; Satélite artificial. ; Tectónico. ; Corteza terrestre inf. ; Corteza continental. ; Deformación finita. ; Antecámbrico. ; Spot. ; Foliación. ; Cinemática. ; Cizalladura. ; ...
Brazilian Journal of Geology, 2015
Journal of African Earth Sciences (1983), 1984
Serpentine minerals in natural samples are dominated by lizardite and antigorite. In spite of num... more Serpentine minerals in natural samples are dominated by lizardite and antigorite. In spite of numerous laboratory experiments, the stability fields of these species remain poorly constrained. This paper presents petrological observations and the Raman spectroscopy and XRD analyses of natural serpentinites from the Alpine paleo-accretionary wedge. Serpentine varieties were identified from a range of metamorphic pressure and temperature conditions from sub-greenschist (P b 4 kbar, T~200-300°C) to eclogite facies conditions (P > 20 kbar, T > 460°C) along a subduction geothermal gradient. We use the observed mineral assemblage in natural serpentinite along with the T max estimated by Raman spectroscopy of the carbonaceous matter in associated metasediments to constrain the temperature of the lizardite to antigorite transition at high pressures. We show that below 300°C, lizardite and locally chrysotile are the dominant species in the mesh texture. Between 320 and 390°C, lizardite is progressively replaced by antigorite at the grain boundaries through dissolution-precipitation processes in the presence of SiO 2 enriched fluids and in the cores of the lizardite mesh. Above 390°C, under high-grade blueschist to eclogite facies conditions, antigorite is the sole stable serpentine mineral until the onset of secondary olivine crystallization at 460°C.
Precambrian Research, 2003
This paper deals with the late Neoproterozoic-Cambrian tectonic evolution of a part of north-cent... more This paper deals with the late Neoproterozoic-Cambrian tectonic evolution of a part of north-central Madagascar, which is characterized by the occurrence of a mafic-ultramafic sequence (the Andriamena unit) overlying a gneissic-granitic basement. The finite strain pattern has been determined by carrying out a SPOT satellite image analysis, structural mapping of specific areas and kinematic analyses of shear zones. Structural investigations reveal the presence of two superposed finite strain patterns, D 1 and D 2 . The D 1 event is related to the emplacement of the Andriamena unit on the top of the gneissic-granitic basement. The western contact between these units is a major mylonitic zone characterized by a non-coaxial strain regime consistent with a top-to-east displacement. We suggest that the Andriamena unit originated as a lower crustal fragment of a middle Neoproterozoic continental magmatic arc related to the closure of the Mozambique Ocean. This fragment was thrusted onto the gneissic-granitic basement after 630 Ma, i.e. the age of emplacement of characteristic stratoid granites found only in the lower unit. The D 2 event is related to east-west horizontal shortening mainly accommodated by F 2 upright folds. In-situ electron microprobe dating of monazites from the Andriamena unit constrains the age of the D 1 and D 2 events between 530 and 500 Ma under amphibolite to granulite-facies conditions (5-7 kbar, 650-700 • C). The eastward thrust emplacement of the Andriamena unit (D 1 ) followed by the horizontal shortening (D 2 ) are ascribed to the same Cambrian tectonic regime (i.e. east-west convergence). Such D 1 -D 2 bulk strain pattern has been recognized throughout Madagascar and at various structural levels of the crust: in the lower crust in Southern Madagascar and in the uppermost crustal level in the SQC unit (central Madagascar). The D 1 -D 2 event is interpreted to result from the continental convergence of the Australia-Antarctica block and the Madagascar, India, Sri Lanka block during the final amalgamation of Gondwana.
Terra Nova, 2013
The abundances of F, Cl and S in arc magmas are systematically higher than in other mantle-derive... more The abundances of F, Cl and S in arc magmas are systematically higher than in other mantle-derived magmas, suggesting that these elements are added from the slab along with H 2 O. We present ion probe microanalyses of F, Cl and S in serpentine minerals that represent the P-T evolution of the oceanic lithosphere, from its serpentinization at the ridge, to its dehydration at around 100 km depth during subduction. F, Cl and S are incorporated early into serpentine during its formation at mid-ocean ridges, and serpentinized lithosphere then car-ries these elements to subduction zones. More than 50% of the F, Cl and S are removed from serpentine during the prograde metamorphic lizardite/antigorite transition. Due to the low solubility of F in water, and to the low amount of water released during this phase transition, the fluids mobilizing these elements must be dominated by SO X rather than H 2 O.
Earth and Planetary Science Letters, 2014
Serpentinites are an important component of the oceanic lithosphere that formed at slow to ultra-... more Serpentinites are an important component of the oceanic lithosphere that formed at slow to ultra-slow spreading centers. Serpentine could thus be one of the most abundant hydrous minerals recycled into the mantle in subduction zones. Prograde metamorphism in subducted serpentinites is characterized by the destabilization of lizardite into antigorite, and then into secondary olivine. The nature of the fluid released during these phase transitions is controlled by redox reactions and can be inferred from oxidation state of Fe in serpentine minerals. We used bulk rock analyses, magnetic measurements, SEM observations and μXANES spectroscopy to establish the evolution of Fe 2 O 3 Tot (BR) and magnetite content in serpentinite and Fe oxidation state in serpentine minerals from ridge to subduction settings. At mid-ocean ridges, during the alteration of peridotite into serpentinite, iron is mainly redistributed between magnetite and oceanic serpentine (usually lizardite). The Fe 3+ /Fe Total ratio in lizardite and the modal percentage of magnetite progressively increase with the degree of local serpentinization to maxima of about 0.8 and 7 wt%, respectively, in fully serpentinized peridotites. During subduction, the Fe 2 O 3 Tot (BR) of serpentinite remains constant (∼7-10 wt%, depending on the initial Fe content of the peridotite) while the modal percentage of magnetite decreases to less than 2% in eclogite facies rocks. The Fe 3+ /Fe Total ratio in serpentine also decreases down to 0.2-0.4 in antigorite at eclogite facies. Our results show that, in the first 70 km of subduction, the transition from lizardite to antigorite is accompanied by a reduction of Fe in bulk rock samples and in serpentine minerals. This redox reaction might be coupled with the oxidation of reduced oceanic phases such as sulfides, and the formation of oxidized fluids (e.g. SO X , H 2 O, CO X ). At greater depths, the beginning of antigorite dehydration leads to an increase of Fe 3+ /Fe Total in relict antigorite, in agreement with the preferential partitioning of ferric iron into serpentine rather than into olivine.
Precambrian Research, 2000
This paper examines the thermo-mechanical evolution of the lower crust, in Precambrian times, wit... more This paper examines the thermo-mechanical evolution of the lower crust, in Precambrian times, with an example from southern Madagascar. The finite strain pattern is derived from the study of satellite images complemented by field structural analysis. The finite geometry reflects the superposition of two distinct finite strain patterns, D1 and D2. The geodynamic significance of the D1 event remains unclear. However, the D2 finite strain pattern is partitioned between a network of kilometric vertical shear zones and folded domains, and is consistent in the Mozambique belt with east-west shortening in a transpressive regime.The metamorphic conditions associated with the two finite strain fields show that rather uniform, high temperatures were ubiquitous in southern Madagascar. By contrast, regional pressure differences were controlled primarily by the major shear zones (D2). Chronological constraints obtained from monazite (U-Th-Pb electron microprobe dating) indicate ages of 590 -530 Ma for the D1 event and 530-500 Ma for the D2 event. The two distinct strain fields D1 and D2 are continuous in time.The late pan-African transpressional tectonic regimes, contemporaneous with granulitic facies metamorphic conditions, resulted in strong strain partitioning between shear zones and folded domains. The D2 transpression was efficient and pervasive enough to exhume pieces of the lower crust. The amount of exhumation was controlled by the D2 strain gradient (amount of pure shear with respect to simple shear).
Lithos, 2006
In the present study, we describe and discuss the geology of aluminous-magnesian granulites and a... more In the present study, we describe and discuss the geology of aluminous-magnesian granulites and associated garnet-bearing charnockitic granulite from the Brejões Dome area, located in the Jequié Block, part of the São Francisco Craton in Bahia, Brazil. Investigation of metamorphic mineral assemblages allows the evaluation of P-T conditions for the formation of these rocks, and therefore to obtain constraints for the better understanding of the geological evolution of the area. We conclude that the rocks from the Brejões Dome area were formed under granulite facies conditions of low to intermediate pressure (5-8 kbar). Temperatures determined in samples of aluminous-magnesian granulites collected away from the dome are in the order of 850°C, similar to those determined elsewhere in the southern part of the Itabuna-Salvador-Curaçá Orogen. However, samples of the same rock type collected close to the Brejões Dome are hercynite + quartz-bearing and record higher temperatures of about 900-1000°C. It is suggested that the intrusion of the Brejões charnockite diapir was responsible for a local increase in temperature above the peak temperature of regional granulite metamorphism.
Journal of Structural Geology, 1999
Quartzo-feldspathic granulites are probably the most intensely studied deep-seated rocks with res... more Quartzo-feldspathic granulites are probably the most intensely studied deep-seated rocks with respect to quartz textures. Few microfabric studies explain crystallographic preferred orientation (CPO) of plagioclase as a result of dislocation motion on the (010) [001] and [100] (Ji and Mainprice 1988) in granulite facies conditions. Diffusion-accomodated grain boundary sliding was described from very fine-grained quartzofeldspathic high-grade mylonites (Behrman and Mainprice 1987). The diffusional creep is also enhanced by the presence of granitic melt (Dell'Angelo and Tullis 1988).
Journal of Petrology, 2004
Petrological studies and electron microprobe dating of monazite from the mafic Andriamena unit, n... more Petrological studies and electron microprobe dating of monazite from the mafic Andriamena unit, north-central Madagascar, indicate that an apparently continuous P-T path inferred for Mg-granulites is actually discontinuous, resulting from the superposition of two distinct metamorphic events at 2Á5 Ga and $750 Ma. The late Archaean event corresponds to an ultrahigh-temperature metamorphism (1000 C, 10Á5 kbar) characterized by a sapphirine-garnet-orthopyroxene-quartz assemblage. Neoproterozoic ages are associated with the development of a sapphirine-cordierite-bearing assemblage, symplectites of orthopyroxene-sillimanite and partial melting at $850 C and 7 kbar. This sequence of reactions and mineral assemblages could be interpreted as the result of near-isothermal decompression to about 4 kbar followed by isobaric cooling to 650 C. However, geodynamic constraints suggest that the granulites underwent a phase of cooling to the stable geotherm following the ultrahightemperature metamorphism at 2Á5 Ga. Consequently, we suggest that the 'petrographical path' inferred from the Mg-granulites is not representative of the actual P-T-t path. The decompression, in particular, is an artefact of the P-T path with no geological meaning; it results from the equilibration of the refractory late Archaean ultrahigh-temperature assemblages at a lower pressure during the middle Neoproterozoic event.
Gondwana Research, 1999
Lobomtoire de PCtrologze, Uniuersite' d' Aiitanaiiariuo, B P 906, M a d a g m x r
Geology, 1997
The external or internal origin of CO 2 and H 2 O in marbles and metabasites from a large-scale g... more The external or internal origin of CO 2 and H 2 O in marbles and metabasites from a large-scale granulite section is related to their structural setting: outside shear zones, within major shear zones ({approx} 25 km wide by> 340 km long), or within minor shear zones (< 10 km ...
Geodinamica Acta, 2000
Paradiso massif (French-Italian Alps). The Piemontese zone, at the western border of the Gran Par... more Paradiso massif (French-Italian Alps). The Piemontese zone, at the western border of the Gran Paradiso massif (western Alps) consists of the oceanic schistes lustrés units and the continental Grand Paradiso (GP) unit. In complement to previous work, tectonometamorphic investigations allow us to establish pressure gaps between the three studied units with: the upper schistes lustrés (LS) unit, metamorphosed under blueschist facies conditions (9.5 ± 2 kbar, 340 ± 30°C). The lower schistes lustrés (LI) unit, metamorphosed under low temperature eclogite facies conditions (12.5 ± 3 kbar, 480 ± 50°C). The Gran Paradiso (GP) unit, metamorphosed under higher pressure and temperature eclogite facies conditions (12 to 20 kbar, 500 ± 50°C). The whole metamorphic pile recorded a decompression under amphibolite facies conditions for the LI unit and in the greenschist facies conditions for the LS unit and GP unit, i.e. with a slight and late temperature increase. Fluid inclusion studies on quartz in late cracks and shear planes (C') show that the three units were juxtaposed and deformed together under metamorphic conditions of 4 ± 1 kbar, and 400 ± 50°C. A finite strain field study reveals regional scale extensional tectonics beginning under greenschist facies conditions and ending under brittle conditions. Ductile greenschist deformation corresponds to dome and basin trajectories of the foliation surface. A partition is observed between domains where a pure shear regime prevails in the core of the domes and domains where a simple shear regime prevails, towards the WNW, at the rim of the domes, at the contact between units. Brittle deformation corresponds to a continuum of the ductile deformation. Meanwhile, metamorphic contrasts suggested by pressure estimates cannot be ruled by the relative extension-related dis-placements. This extension corresponds to the accommodation of the vertical indentation of the high pressure units by the stacking of deep crustal slices, in front of the rigid Apulian mantle back-stop, during continuous convergence. © 2000 Éditions scientifiques et médicales Elsevier SAS French-Italian Alps / HP metamorphism / exhumation / synconvergence extension / vertical pinching Résumé -À la bordure occidentale du massif du Grand Paradis (Alpes occidentales), la zone Piémontaise est constituée des unités océaniques des schistes lustrés et de l'unité continentale du Grand Paradis. Une étude métamorphique nous permet de préciser et de discuter des discontinuités de pression et des conditions de rétromorphose de trois unités piémontaises déjà distinguées antérieurement. L'unité supérieure des schistes lustrés (LS) métamorphisée dans le faciès des schistes bleus (9.5 ± 2 kbar, 340 ± 30°C). L'unité inférieure des schistes lustrés (LI) métamorphisée dans le faciès des éclogites (12.5 ± 3 kbar, 480 ± 50°C). L'unité continentale du Grand Paradis (GP) métamorphisée dans le faciès des éclogites de plus haute pression (12 à 20 kbar, 500 ± 50°C). L'ensemble des unités enregistre une décompression dans les conditions du faciès amphibolite à épidote, et donc avec une légère augmentation tardive de température, pour les unités LI et GP, et dans celles des schistes verts pour l'unité LS. L'étude des inclusions fluides dans les fentes de tension et dans les plans de cisaillement, en parallèle à l'étude des paragenèses rétromorphiques permet de montrer que c'est tardivement (4 ± 1 kbar, 400 ± 50°C) que l'histoire tectonométamorphique devient commune à l'ensemble des unités. L'étude du champ de la déformation finie met en évidence une tectonique en extension qui débute en conditions ductiles dans le faciès amphibolite à épidote pour LI, et schiste vert pour LS, et se poursuit en conditions fragiles. La déformation ductile se traduit par des trajectoires en dômes et bassins de la foliation, avec une partition entre des * Correspondence and reprints:
Geodinamica Acta, 2000
The North Caribbean margin is an example of an oblique convergence zone where the currently expos... more The North Caribbean margin is an example of an oblique convergence zone where the currently exposed HP-LT rocks are systematically localised close to strike-slip faults. The petrological and structural study of eclogite and blueschist facies rocks of the peninsula of Samaná (Hispaniola, Dominican Republic) confirms the presence of two different metamorphic units. The former diplays low metamorphic grade (Santa Barbara unit), characterized by the assemblage albite -lawsonite (7.5 ± 2 kbar and 320 ± 80°C). The latter (Punta Balandra unit), thrust over the first unit towards the NW, and is characterized by the occurrence of blueschist and eclogite facies assemblages (13 ± 2 kbar and 450 ± 70°C), within oceanic metasediments. The isothermal retrograde evolution occurred in epidote-blueschist facies conditions (9 ± 2 kbar and 440 ± 60°C). The late greenschist facies evolution is contemporaneous with conjugate NW-SE extension and E-W strike-slip faulting. This late extension is for regional dome and basin structures. According to their lithotectonic, structural and metamorphic characteristics, the metamorphic nappe stack of Samaná may be interpreted as a fragment of an accretionary wedge thrust onto the North American continental shelf. Evolution of the wedge was associated with the active subduction of the North American plate, under the Greater Antilles arc, at the level of the Puerto Rico trench. During active Late Cretaceous convergence, the HP rocks were initially exhumed, within the accretionary prism, by thrusting parallel to the NE-SW direction of convergence. Subsequently, during the Eocene collision between the Caribbean plate and the North American margin, the installation of a transtensive regime of E-W direction supports the local development of conjugate extension of NW-SE direction that facilitated the final phase of exhumation of the HP rocks. © 2000 Éditions scientifiques et médicales Elsevier SAS subduction / exhumation / extension / strike-slip fault / North Caribbean margin / HP-LT metamorphism / accretionary wedge -119 -Éocène, entre la plaque Caraïbe et la marge nord-américaine, la mise en place d'un régime global transtensif senestre de direction Est-Ouest favorise le développement local d'une extension conjuguée de direction NW-SE permettant la fin de l'exhumation des roches de haute pression. © 2000 Éditions scientifiques et médicales Elsevier SAS subduction / exhumation / extension / décrochements / marge Nord-Caraïbes / métamorphisme de haute pression / basse température / prisme d'accrétion P. Goncalves et al.
European Journal of Mineralogy, 2001
The thermal history of a mafic xenolith from the Beaunit maar (Massif Central, France) is reconst... more The thermal history of a mafic xenolith from the Beaunit maar (Massif Central, France) is reconstructed at the basis of a transmission electron microscopy study. The protolith is a meta-microgabbro (opx-1, cpx-1, pl-1) sampled in the lower continental crust (T = 870-970°C, P 0.7-0.8 GPa). The incorporation in the basaltic magma produced five reactions around orthopyroxene: opx-1 Þ cpx-2 Þ cpx-3 (augite + high pigeonite) Þ liq Þ cpx-4. The final reaction is the transformation of residual cpx-3 (augite + high pigeonite) into cpx-5 (augite + low pigeonite). The calculation of the time required for each transformation yields a minimum residence time of the enclave in the host magma of 16 hours and a magma ascent velocity of 1.8 km.h -1 . Exsolutions are produced by pressure decrease as the xenolith is brought up to the surface in the host basalt. Fractures observed in primary minerals are interpreted as a consequence of xenolith shocks against the wall of the magma conduit.
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Papers by Christian Nicollet