Hervé Diot

• La Rochelle Université

The Saghro inlier in the Anti-Atlas belt of Morocco comprises several granitoids dating from 600 to 550 million years ago (Ma), which are overlain by a volcano-sedimentary series. In particular, the granodioritic plutons exhibit widespread enclaves, which is a Tool for emplacements mode and magma interaction processus during the Ediacaran evolution...

The Camarat Granitic Complex (CGC), emplaced in the migmatitic Internal Zone of the Maures–Tanneron Massif (MTM), SE Variscides, consists of the Gigaro granodiorite and the composite Camarat granite. U‐Pb dating of the latter gives crystallization ages of 304.5 ± 3.3 Ma (zircon date) and 303.5 ± 4.0 Ma (monazite date). Two representatives of late f...

Le gisement de Talc de Nkob, situé au Sud-Est de la boutonnière de Sirwa dans l'Anti-Atlas central, est encaissé dans les métacarbonates du groupe de Taghdout en contact avec le granite édiacarien d'Amassine. Il se présente sous forme d'une lentille stratiforme au sein de laquelle s'alternent des bancs décimétriques à métriques de marbres, de talci...

The Nkob talc deposit located in the central Anti-Atlas Pan-African belt is hosted by magnesian and siliceous metacarbonates in the contact aureole of the Ediacaran Amassine granite. It consists of a stratified succession of green serpentine-rich marbles, black dolomitic marbles, talcitites and phlogopitites (variously retrogressed into chloritites...

The southwestern French Massif central in western Rouergue displays an inverted metamorphic sequence with eclogite and amphibolite facies units forming the top of the nappe stack. They are often grouped into the leptyno-amphibolite complex included, in this area, at the base of the Upper Gneiss Unit. We sampled garnet micaschists and amphibolites t...

Anisotropy of magnetic susceptibility data validated by image analysis were acquired on the Sept Îles Layered Intrusion. Most data come from the mafic Layered Series of the intrusion, although the overlying anorthositic Upper Border Series and felsic Upper Series were also investigated. In the Layered Series, Type 1 magnetic fabric defined by gentl...

This work provides the first comprehensive petrological and multi-scale structural investigation of a suite of ultramafic bodies and enclosing metasediments from the Late Paleozoic accretionary prism of South-Central Chile. The targeted outcrops are located in the La Cabaña area and are characterized by the presence of three main types of ultramafi...

El presente trabajo investiga rocas máficas de un cuerpo de 3 km2 en la Loma Guzmán, a ~2 km del cuerpo ultramáfico de Centinela Bajo Norte, en rocas cajas de mica-esquistos. Esto, mediante estudios petrológicos, análisis de química mineral y condiciones metamórficas de rocas máficas cercanas al cuerpo serpentinítico de La Cabaña (IX Región). Las c...

The basement of the Alpine Upper Danubian/Balkan nappe, dismembered between Romania, Serbia and Bulgaria, contains evidence of the Variscan orogenic evolution (Lower Devonian Balkan-Carpathian ophiolite, Carboniferous granites). Our study presents a new tectono-metamorphic interpretation of this basement and documents two main deformation phases, D...

The Kleivan and Sjelset granitic complexes are two composite plutons, containing both orthopyroxene and biotite (± hornblende) facies, emplaced in the Sveconorwegian (Grenvillian) high-grade basement of SW Norway. A structural study of these two plutons, based on the anisotropy of magnetic susceptibility (AMS) technique and combined with high-preci...

The Pan-African belt of North and West Africa exposes world-class remnants of oceanic and continental arcs along the West African craton (WAC) northern and eastern sutures. In the Anti-Atlas domain, ocean-ocean subduction was active between 760 and 640 Ma and magmatism occurred mostly during flare ups (760-740 Ma; 710-690 Ma; 660-640 Ma). Neoproter...

The 2·7 Ga Iguilid mafic intrusion is a post-metamorphic plutonic body made of cumulate gabbronorite and norite characterized by limited variations in modal proportions but significant disparities in trace element contents. The cumulates display microtextural evidence for syn-magmatic deformation, leading to reorientation of cumulus minerals, inden...

The pre-Alpine basement of the Southern Carpathians/Western Balkans contains four ophiolitic massifs dismembered by Alpine tectonics, which define the “Balkan-Carpathian Ophiolite” (BCO) for which the tectonic setting and age of formation are still debated (Precambrian or Early Devonian). In this contribution, we demonstrate that, in light of a Pre...

Many intra-oceanic paleo-arcs are exposed in the Pan-African belt surrounding the West African Craton. In the Moroccan Anti-Atlas, remnants of Intra-Oceanic Subduction Zone (IOSZ) are preserved in few erosional windows moulded along the Anti-Atlas Major fault. These complexes highlight a Neoproterozoic paleo-suture made of 760 My back-arc ophiolite...

The 616 ± 3 Ma (Ediacaran) Egersund doleritic dike swarm cuts across the Rogaland anorthosite province and its granulitic country rocks, in SW Norway. The structure of eight out of eleven main dikes of the swarm was investigated using the anisotropy of magnetic susceptibility (AMS) technique. Thermomagnetic data and values of the bulk magnetic susc...

The Pan-African belt of West and North Africa exposes many intra-oceanic arc complexes while they are rather uncommon in Phanerozoic orogenic belts. Intra-Oceanic Subduction Zone (IOSZ) in the Moroccan Anti-Atlas crop out in two tectonic windows moulded along the Anti-Atlas Major fault: the Sirwa (western-) and the Bou Azzer (eastern-part) inliers,...

Our study concerns deformed gabbroic rocks from the Balkan Carpathian Ophiolite (BCO - Romania, Serbia, Bulgaria). The BCO consists of four ophiolitic massifs dismembered during Alpine tectonic and displaying together a complete classical oceanic lithosphere. Our new Sm-Nd dating on fresh lower gabbroic rocks give an accretion age for the BCO crust...

The Archean Guelb el Azib layered complex (GAC) in the West African craton of Mauritania is composed of an association of serpentinites, chromitites, amphibolites and anorthosites with few fine-grained amphibolite dykes. The complex forms tectonic slices in 2.9-3.5 Ga TTG gneiss terrains in close association with supracrustal rocks (BIFs, impure ma...

The magnetite fabrics measured by anisotropy of magnetic susceptibility (AMS) and by shape preferred orientation (SPO) optical methods are classically used as flow kinematics indicators in lava flows. The development of magnetite fabrics during simple shear strains γ ≤ 20 was performed using a suspension of 1% volume fraction of multidomain magneti...

a b s t r a c t The Carboniferous Cherbelezu batholith (Alm aj Mountains, Romania) is a well-preserved but poorly studied intrusion belonging to the Upper Danubian Alpine Nappe. This pluton crops out along a pre-existing major verticalized formation, the Corbu Mylonitic Zone (CMZ). Our study investigates the role of the CMZ on the deformation recor...

Central Andean deformation history in southern Peru is recorded in Neogene volcanic units of Ocoña and Cotahuasi canyons that cut across the western Cordillera. Acceleration (<25 Ma) of uplift in the region is reflected in the Neogene epiclastic deposits with interspersed and subsequent rhyolitic ignimbrites between 24.6 and 1.37 Ma. Large-volume (...

The Lac Tio hemo-ilmenite ore body is a magmatic ilmenite deposit that crops out in the 1.06 Ga Lac Allard anorthosite which is part of the Havre-Saint-Pierre anorthosite suite, one of many AMCG (Anorthosite-Mangerite-Charnockite-(rapakivi) Granite) suites from the Grenville province of North America. It is the world's largest hard-rock ilmenite de...

The ca. 930–920 Ma Rogaland anorthosite province of Southwest Norway is cross cutted by up to several-km-long dykes of the jotunite kindred. The fabric of three major jotunitic dykes from this igneous complex (the Vetteland, Varberg and Lomland dykes) is investigated here, using measurements of the anisotropy of magnetic susceptibility (AMS) made a...

The ca. 930 Ma Farsund intrusion (SW Norway) belongs to a series of 0.99-0.92 Ga post-collisional plutons from the Sveconorwegian (Grenvillian) orogen. It is made of two rock facies (charnockite and quartz mangerite, and subordinate quartz monzonite and quartz monzodiorite) that show mingling relationships. As shown elsewhere, these two facies belo...

The ca. 930 Ma Farsund intrusion (SW Norway) belongs to a series of 0.99e0.92 Ga post-collisional plutons from the Sveconorwegian (Grenvillian) orogen. It is made of two rock facies (charnockite and quartz mangerite, and subordinate quartz monzonite and quartz monzodiorite) that show mingling relationships. As shown elsewhere, these two facies belo...

The emplacement conditions for 39 igneous dikes cutting basalts in northwestern Ethiopia are evaluated by analyzing their displacement-length scaling relations. Maximum opening displacements and lengths of the A dikes demonstrate displacement-length scaling of the form D(max)=0.088L(0.48), consistent with other populations of dikes and veins and di...

Anisotropy of magnetic susceptibility (AMS) data analysis is a convenient method used to investigate strain and flow during lava flow emplacement. In order to make a sound interpretation, the origin of the AMS signal must be verified. Two questions must be answered: 1) what phase, or phases carry the AMS signal and 2) when was the AMS fabric acquir...

A detailed structural study of the Central Cameroon Shear Zone (CCSZ) segment, in the Bamoun plateau (BP) and the Tikar plain (TP) (West Cameroon), reveals a complex strain geometry of this shear zone. It shows thick mylonite bands wrapping around lenses of various country rock types, at small, medium and large scales. The mylonite foliation trends...

The Motru Dyke Swarm intrudes the Precambrian Danubian basement of the Southern Carpathians (Romania). It is a marker of a sub-volcanic event that occurred during the early Palaeozoic (Cambrian to Ordovician). The geographical distribution of dykes on a ∼2,000km2 area is heterogeneous; several areas of high dyke density have been the subject of a d...

We describe the first occurrence in the Variscan Belt of Western Europe of the relatively rare phosphate wagnerite, ideally Mg2PO4F. It occurs in albite-rich, cordierite-gedrite-bearing gneisses on the island of Ile d'Yeu, southern Armorican Massif, France. These gneisses are associated with a network of shear zones that crosscut granitoid orthogne...

Anisotropy of Magnetic Susceptibility (AMS) is a convenient method for finding strain and thus emplacement information on lava flows. However, interpretation of AMS parameters requires caution and several factors need verification to avoid misunderstandings. Verification can be divided into 2 groups: 1) what minerals create AMS? 2) how AMS behaves?...

carte géologique - publisher: Service de la Carte Géologique du BRGM

Two dykes of different thickness (5.5 m for TJ31 and 23 m for TJ34) from the late Pan-African calc-alkaline Motru Dyke Swarm (S. Carpathians, Romania) have been studied by electron microprobe (mineral chemistry), crystal size distribution (CSD), anisotropy of magnetic susceptibility (AMS) and whole-rock geochemistry. All the physical and chemical v...

We describe amphibolite-facies shear zones affecting an orthogneiss from the Armorican Hercynian belt (Ile d’Yeu, western France). The deformation pattern is consistent with top-to-the-South thrusting followed by E–W extension, as documented elsewhere in the region. Shearing was accompanied by channelled fluid flow that transformed the orthogneiss...

A Late Pan-African calc-alkaline dike swarm (basalt-andesite-dacite-rhyolite) has been investigated in a region of over 2000 km(2) in the Alpine Danubian window, South Carpathians (Romania). Amphibole phenocrysts and microphenocrysts have been investigated by wavelength-dispersive microprobe analysis and BSE imaging. The Ca-amphibole population, re...

Two dykes of different thickness (5.5m for TJ31 and 23m for TJ34) from the late Pan-African calc-alkaline Motru Dyke Swarm (S. Carpathian, Romania) have been studied by electron microprobe (mineral chemistry), Crystal Size Distribution (CSD), Anisotropy of Magnetic Susceptibility (AMS) and whole rock geochemistry. All the physical and chemical vari...

Service de la Carte Géologique du BRGM, sous-presse

The fabric in a dike is representative of the magmatic flow, considered as Newtonian. The anisotropy of magnetic susceptibility of the rocks gives a good representation of the shape-preferred orientation which, in turn, is a marker of the magmatic flow. Generally, a symmetrical pattern of the fabric across the dike is in agreement with a flow of ma...

The Variscan Querigut Pluton (eastern Axial Zone, Pyrenees), recently dated at 307 ± 2 Ma, is a classical example for the structural study of granitoids. We present a new structural analysis of this pluton using the powerful technique of magnetic susceptibility anisotropy (AMS). A model of pluton emplacement is proposed on the basis of complementar...

The Tellnes ilmenite deposit, a world class titanium deposit, occurs in the Åna–Sira anorthosite (Rogaland anorthosite province, South Norway). It is mainly made up of an ilmenite-rich norite that has been previously interpreted as injected in a crystal mush state, in a weakness zone of the enclosing anorthosite. This emplacement mechanism has prod...

The Holum granite (Vest-Agder, southernmost Norway) has been considered to be the oldest (980 Ma) undeformed (“post-tectonic”) pluton of a late-Sveconorwegian granitoid series that form two belts in southern Norway and SW Sweden. An integrated structural study of this granite pluton, based on a survey of its anisotropy of low-field magnetic suscept...

In the Sveconorwegian orogenic province of SW Scandinavia, abundant late-to post-tectonic granitoids intruded between c.a. 990 and 880 Ma, at the end of the Sveconorwegian (= Grenvillian) orogeny. These granitoids form two N-S trending, broad belts of plutons that are parallel to major lithospheric weakness zones dividing the Sveconorwegian provinc...

The Bjerkreim-Sokndal intrusion (BKSK) belongs to the Proterozoic Rogaland igneous complex of Southwest Norway. The BKSK displays an anorthosite to mangerite cumulate series, folded into a syncline, in the core of which crop out massive acidic rocks of quartz mangerite to charnockite composition. We present a study which focuses on the acidic rocks...

We summarise numerical and analogue models of shape fabrics, and discuss their applicability to the shape preferred orientation of crystals in magmas. Analyses of flow direction and finite strain recorded during the emplacement of partially crystallised magmas often employ the analytical and numerical solutions of the Jeffery's model, which describ...

We summarise numerical and analogue models of shape fabrics, and discuss their applicability to the shape preferred orientation of crystals in magmas. Analyses of flow direction and finite strain recorded during the emplacement of partially crystallised magmas often employ the analytical and numerical solutions of the Jeffery's model, which describ...

Ideal populations of crystals in viscous magmas display cyclic shape preferred orientations (SPO). In theory, this should allow the determination of paleo-flow directions by the detection of obliquities between grain populations of different shape. However, analogue experiments and simple calculations indicate that the cyclicity of different shape...

Magmas flowing during their emplacement are considered to be suspensions of rigid particles crystallising progressively in a viscous medium submitted to a simple shear deformation. The question is, how flow history in terms of direction and intensity of shear, can we inferred from the directional properties of mineral shape fabric developed during...

A study of the Neogene low-aspect-ratio Kizilkaya ignimbrite (in the calc-alkaline Central Anatolian Volcanic Province, Turkey) has been carried out using the anisotropy of magnetic susceptibility (AMS) technique on 46 sites. IRM, hysteresis loops and Curie temperature analysis indicate that magnetite is the main carrier of the magnetic signal in t...

Deformation in the Bjerkreim-Soknadal layered intrusion apophysis was developed continuously from magmatic to solid state. The tectonic setting dictating these deformations was dominated by anorthosite diapirism. An anisotropy of magnetic susceptibility (AMS) study has been performed in the northern part of this apophysis. It shows that titanomagne...

Deformation in the Bjerkreim-Sokndal layered intrusion apophysis was developed continuously from magmatic to solid state. The tectonic setting dictating these deformations was dominated by anorthosite diapirism. An anisotropy of magnetic susceptibility (AMS) study has been performed in the northern part of this apophysis. It shows that titanomagnet...

The theory of the rotation of isolated rigid particles within a linearly viscous fluid deforming in progressive simple shear is often invoked in models of Shape Preferred Orientations (SPO) of crystals in igneous rocks. A classical result of the theoretical model is that the SPO should rotate and pulsate with increasing strain, with a periodicity e...

Experimental simple shear with γ ≤ 20 was applied to three-dimensional shape fabrics of biotite grains embedded in a viscous matrix. This used a ring-shear apparatus deforming a medium made of silicone + plasticine + biotite grains at room pressure and 50°C temperature. The low-field anisotropy of magnetic susceptibility characterised the fabric of...

Jeffery's equations ascribe a theoretical cyclic nature to the shape fabric of non-interacting rigid particles immersed in a viscous fluid undergoing simple shear flow. This theoretical behaviour is confirmed at ‘low’ shear strains (γ < 6) by two-dimensional experiments in a torsion apparatus, inducing shape fabric development of particles evenly d...

Tridimensional experiments of magmatic fabric have been produced using natural paramagnetic crystals of amphiboles (200 µm<φ<300 µm) within a diamagnetic viscous fluid (boropolysiloxane + plasticine). The apparatus used, similar to the Couette viscometer, is composed by two counter rotational cylinders which were chosen to ensure high homogeneous s...

The High-Moulouya granites from Aouli and Bou-Mia contain magmatic structures, generated during emplacement in the crust, which provide evidence for laccolithic injection. The first magmas, injected along normal faults, were gabbroic in composition and cause a partial melting of pelitic country-rocks. Evidence for magmatic mixing is provided by var...

The magnetic structures of the Petit Gerbier phonolitic neck have been studied by the Anisotropy of Magnetic Susceptibility (AMS), revealing its internal organization (foliations and lineations). Results of the AMS are microstructurally checked by studies of shape preferred orientations of minerals, and image analysis using the intercept method. Th...

The concentrically zoned Zaër pluton (Variscan Meseta of Morocco), previously modeled as the nesting of two magmas forming a ballooning pluton, is here subjected to a study of its internal magmatic and solid-state structures. The magmatic flow patterns, derived mainly from anisotropy of magnetic susceptibility measurements, together with structural...

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The magmatic structures of the Bou-Mia and Aouli granitoid massifs that outcrop in the Upper Moulouya window (eastern Morocco) have been studied using the anisotropy of their magnetic susceptibility (AMS). For both massifs, the mean magnetic foliation has a subhorizontal to moderate dip, with a zonal orientation around the SE-NW subhorizontal direc...

Mapping and structural study of the Central Rehamna lead us to ascertain the volcanic basement of the Cambrian basal series. We specify the lithostratigraphy of this region, correlative with less deformed and fossiliferous sequences outcropping just to the W. Originating in Cambrian times, the Central Rehamna is a shoal which greatly influences the...

The Lanvaux-Les-Ponts-de-Ce anticline structure is a narrow elongate zone trending N110oE in direction, where pre-Llanvirnian and middle Ordovician schist formations outcrop. It is here considered as a ductile zone according to the plasticity of quartz, being active in Hercynian times (between 345 and 320Ma) under greenschist facies temperature con...